feature: create extendable eslint config

[joshuagraber]

Resolves #40

To test already-implemented eslint config (This has already been published as a sub-package, @pdap-design-system/eslint-config)

1. Visit this PR to data-sources
   and observe successful linting workflow run.
2. To test locally, check out the PR, cd client and npm run lint.
3. To test IDE integration, ensure you're using VS Code or another editor that has eslint and prettier extensions configured. In any js or vue file, find a string with single quotes and change it to use double quotes. Save the file. Ensure the string is auto-formatted to use single quotes again.

[josh-chamberlain]

I'm stuck at step 3 — I'm reasonably sure I know what "add eslint" means but I definitely don't know what "Extend @pdap-design-system/eslint-config" means. Perhaps having Marty review would make more sense?

[joshuagraber]

@josh-chamberlain Yes, I can see how this is unclear, sorry about that. And really, following the instructions in that issue is probably overkill for testing this anyways. I'll update in the morning with simpler, clearer AC.

[joshuagraber]

@josh-chamberlain @mbodeantor updated the testing steps. Given that I already published the sub-package to npm and integrated into my PR to data-sources for linting and client stuff in CI, the results of this PR are observable in my PR there.

[github-actions]

🎉 This PR is included in version 2.2.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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