Github action for linting and running unit tests

[MattGeri]

When a PR is created, a Github action should be fired to run linting (PHPCS/WPCS and JSLint/ESLint). Unit tests should also be run. A PR should not be able to be approved until the lints/tests are successful.

[jeffpaul]

https://github.com/10up/wpcs-action might be helpful on the PHPCS/WPCS front. The work in 10up/simple-podcasting#117 may be helpful for acceptance tests. https://github.com/10up/classifai/blob/develop/.github/workflows/lint.yml shows options for linting.

[MattGeri]

Thanks @jeffpaul! 🚀