Migrate Travis jobs to GitHub actions

[ravichdev]

Summary

• PHP unit tests use a modified script to download WP and WP unit tests. We could look into moving this file to wp-dev-lib
• The PHP tests use the base ubuntu-* image to run PHP tests, using docker to run these tests will increase the time.
• The build is pretty fast now except for the E2E tests which use docker images and npm run env:start to setup local docker env and this is resulting in the job taking ~4 minutes. This could also be improved if we use apache or nginx bundled in the base ubuntu-* image instead of docker.

Test PR actions - https://github.com/ravichdev/wp-foo-bar/actions/runs/684218426

Fixes #

Checklist

• [ ] My pull request is addressing an open issue (please create one otherwise).
• [ ] My code is tested and passes existing tests.
• [ ] My code follows the Contributing Guidelines (updates are often made to the guidelines, check it out periodically).

[ravichdev]

@derekherman @kasparsd This is ready for review.

[spacedmonkey]

@ravichdev I have posted some thoughts here. I have a lot of experience with github actions. We can copy and paste lots of work done elsewhere, like in web stories.

Also, can we enable github actions, see can these running.