Add linting GitHub Action workflows

[dkotter]

Description of the Change

Adds our (semi) standard GitHub Action linting workflows.

Historically we've had a single lint.yml workflow that has jobs for eslint and PHPCS. I've broken those into two different workflow files here so we can utilize GitHub Actions path filtering to only run those actions when either JS or PHP files have been changed respectively.

We've talked about wanting to make these sorts of changes across all of our plugins (being smarter on when Actions run) so figured it was worth putting that effort in here and we can copy this approach across to other plugins as we see fit.

The PHPCS Action does the following:

• Runs anytime a PR is opened against develop or code is pushed to develop or trunk
• Only runs if PHP files have been changed
• Sets up PHP version 7.4 (our minimum), runs composer install and then lints any changed lines within the changed PHP files

The eslint Action does the following:

• Runs anytime a PR is opened against develop or code is pushed to develop or trunk
• Only runs if JS files have been changed
• Sets up Node to match what's in our .nvmrc (v18 right now), runs an npm install and then uses 10up-tookit to lint any changed JS files

Most of our plugins don't use 10up-toolkit, they use wp-scripts, so some slight adjustments on the eslint workflow will be needed if we copy these changes across.

Closes #13

How to test the Change

Can see a commit with no PHP or JS changes here: https://github.com/10up/block-catalog/pull/20/checks?sha=9cb38084248909fa40b2ac5f7768b5f618eddf38

Can see a commit with a failing PHPCS check here: https://github.com/10up/block-catalog/pull/20/checks?sha=6ca435ccd683854226cf81f3fef620eaf174671b

Can see a commit with a failing eslint check here: https://github.com/10up/block-catalog/pull/20/checks?sha=4bce3a60ea78d14eb3dc3aef8371b4931aadd06b

And a commit with all checks passing: https://github.com/10up/block-catalog/pull/20/checks?sha=e62f072523b3bcd831a90fa0daa925919ed0d81e

Changelog Entry

Added - GitHub Action workflows to lint our PHP and JS files.

Credits

Props @dkotter

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[jeffpaul]

Looks good to me, thanks!