Make resource and artifact paths in bundle config relative to config folder

[andrewnester]

Warning: breaking change

Changes

Instead of having paths in bundle config files be relative to bundle root even if the config file is nested, this PR makes such paths relative to the folder where the config is located.

When bundle is initialised, these paths will be transformed to relative paths based on bundle root. For example,
we have file structure like this

- mybundle
| - bundle.yml
| - subfolder
| -- resource.yml
| -- my.whl

Previously, we had to reference my.whl in resource.yml like this, which was confusing because resource.yml is in the same subfolder

sync:
  include:
    - ./subfolder/*.whl
...
tasks:
  - task_key: name
    libraries:
      - whl: ./subfolder/my.whl
...

After the change we can reference it like this (which is in line with the current behaviour for notebooks)

sync:
  include:
    - ./*.whl
...
tasks:
  - task_key: name
    libraries:
      - whl: ./my.whl
...

Tests

Existing translate_path_tests successfully passed after refactoring.

Added a couple of uses cases for Libraries paths.

Added a bundle config tests with include config and sync section

[pietern]

Two thoughts on the selector/transformer approach:

• They are the same except for the directory relative to which the rewrite should happen. I think this doesn't warrant two separate structures. Perhaps the dir can be passed through to the functions that produce the selectors (and be made to return instances of a transformer)?
• The rewriteFunc already does a filepath.Rel to determine how the path is relative to the given directory. The same is happening in translateToBundleRootRelativePath. Can these be consolidated? Right now we're mixing up what seems to be 1) making paths relative to the bundle root, and 2) rewriting them into remote paths. If we break this up into doing 1 first and 2 second, then I suspect things to be clearer.

[andrewnester]

@pietern

1. Agree on the selectors / transformers logic, simplified it and removed the selectors
2. Slightly refactored rewriteFunc and now we have transformNoOp which won't do anything and just return local relative path, it should make the intentions clearer.