refactor: use custom eslint config + prettier instead of airbnb config

[malept]

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• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes have sufficient test coverage (if applicable).

Summarize your changes:

Switch from the airbnb eslint config to one that should be more in line with the rest of the Electron tooling that doesn't use StandardJS.

Please note that prettier is configured to use single quotes instead of double quotes. This is mostly because I didn't want an even larger diff.

Added some test scripts to individual modules to run tests in isolation.

While fixing TypeScript types, I fixed a bug in the Forge 5 ➡️ Forge 6 upgrader that used the wrong key name for make targets.

[codecov]

Codecov Report

Merging #2520 (da6a0dc) into master (bc0ed95) will decrease coverage by 0.18%.
The diff coverage is 65.48%.

@@            Coverage Diff             @@
##           master    #2520      +/-   ##
==========================================
- Coverage   72.89%   72.71%   -0.19%     
==========================================
  Files          91       91              
  Lines        2365     2349      -16     
  Branches      448      429      -19     
==========================================
- Hits         1724     1708      -16     
  Misses        471      471              
  Partials      170      170              

Impacted Files	Coverage Δ
packages/api/cli/src/electron-forge.ts	58.06% <0.00%> (ø)
...ges/api/core/src/api/init-scripts/find-template.ts	95.23% <ø> (ø)
...es/api/core/src/api/init-scripts/init-directory.ts	93.75% <0.00%> (ø)
packages/api/core/src/api/lint.ts	66.66% <0.00%> (-2.57%)	⬇️
packages/api/core/src/util/plugin-interface.ts	31.11% <ø> (ø)
packages/api/core/src/util/require-search.ts	85.71% <0.00%> (ø)
packages/installer/base/src/Installer.ts	75.00% <ø> (ø)
packages/installer/darwin/src/InstallerDarwin.ts	33.33% <0.00%> (ø)
packages/installer/deb/src/InstallerDeb.ts	33.33% <ø> (ø)
packages/installer/dmg/src/InstallerDMG.ts	25.00% <0.00%> (ø)
... and 65 more

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