chore(lint): fix eslint issues in src/routes

[pano9000]

Fix eslint issues reported for src/routes

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/attachments.ts
  36:38  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  44:29  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/clipper.ts
   33:11  error  'title' is never reassigned. Use 'const' instead      prefer-const
   33:18  error  'content' is never reassigned. Use 'const' instead    prefer-const
   33:36  error  'images' is never reassigned. Use 'const' instead     prefer-const
   64:26  error  Unexpected any. Specify a different type              @typescript-eslint/no-explicit-any
  103:18  error  'content' is never reassigned. Use 'const' instead    prefer-const
  103:36  error  'images' is never reassigned. Use 'const' instead     prefer-const
  103:54  error  'labels' is never reassigned. Use 'const' instead     prefer-const
  222:9   error  'pageUrl' is never reassigned. Use 'const' instead    prefer-const
  224:9   error  'foundPage' is never reassigned. Use 'const' instead  prefer-const

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/export.ts
  40:17  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/image.ts
  85:11  error  'note' is assigned a value but never used. Allowed unused vars must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/import.ts
   71:17  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  123:17  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/recent_changes.ts
  8:15  error  'RevisionRow' is defined but never used. Allowed unused vars must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/relation-map.ts
  33:40  error  'noteId' is defined but never used. Allowed unused args must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/revisions.ts
    4:8   error  'revisionService' is defined but never used. Allowed unused vars must match /^_/u  @typescript-eslint/no-unused-vars
  114:9   error  'allNoteIds' is never reassigned. Use 'const' instead                              prefer-const
  148:42  error  Unexpected any. Specify a different type                                           @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/script.ts
  12:13  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  36:17  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/similar_notes.ts
  11:11  error  'note' is assigned a value but never used. Allowed unused vars must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/sql.ts
  59:17  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/sync.ts
  33:17  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api_docs.ts
  1:28  error  'Router' is defined but never used. Allowed unused vars must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/assets.ts
  8:104  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  8:124  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/custom.ts
  28:21  error  Unexpected any. Specify a different type                                @typescript-eslint/no-explicit-any
  48:25  error  Unexpected any. Specify a different type                                @typescript-eslint/no-explicit-any
  71:64  error  'next' is defined but never used. Allowed unused args must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/electron.ts
  10:17  error  The `{}` ("empty object") type allows any non-nullish value, including literals like `0` and `""`.
- If that's what you want, disable this lint rule with an inline comment or configure the 'allowObjectTypes' rule option.
- If you want a type meaning "any object", you probably want `object` instead.
- If you want a type meaning "any value", you probably want `unknown` instead  @typescript-eslint/no-empty-object-type

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/error_handlers.ts
   5:19  error  Unexpected any. Specify a different type                                @typescript-eslint/no-explicit-any
  20:17  error  Unexpected any. Specify a different type                                @typescript-eslint/no-explicit-any
  25:19  error  Unexpected any. Specify a different type                                @typescript-eslint/no-explicit-any
  25:53  error  'next' is defined but never used. Allowed unused args must match /^_/u  @typescript-eslint/no-unused-vars

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/routes.ts
  480:130  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any
  496:29   error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

✖ 38 problems (38 errors, 0 warnings)
  3 errors and 0 warnings potentially fixable with the `--fix` option.

fixes all of the above errors, except for:

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/clipper.ts
  64:26  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

/home/pano/Programming/0_repos/TriliumNextNotes/src/routes/api/script.ts
  12:13  error  Unexpected any. Specify a different type  @typescript-eslint/no-explicit-any

✖ 2 problems (2 errors, 0 warnings)

as I do not fully understand what form these any types can take

——

This PR also includes two changes which are not strictly linting related, but helped fix those errors.
I hope it's ok to just include them in this PR anyways.

They both have to do with the way we check for errors in the try/catch blocks.
Since in JS you can throw anything, we need to make sure that we are dealing with an actual Error instance, before we can use the message and stack properties.

a) I've added a HttpError class, which extends from the Error class, and made the ValidationError and NotFoundError extend from HttpError class – this makes handling these errors a bit easier, as these errors are now instances of Error.
b) I've added an safeExtractMessageAndStackFromError to extract the message and stack properties from an "unknown" type error - it will check if the error is of instance Error, and return these. If it isn't it will use fallback strings. This get rid of code duplication in all of these error blocks.