GitHub Actions CI

[callmecampos]

Testing Warehouse using GitHub Actions. We run all of our jobs in parallel using the native ubuntu-latest Docker containers provided by GitHub Actions.

• The testing job runs inside of a PostgreSQL service container, specifically postgres:10.1 instead of postgres:latest.
• Ideally we would cache Docker containers with GitHub Package Registry instead of Docker Hub (because of faster build time when compared to other caching methods), however it doesn't yet seem possible to use for container actions because accessing even public packages on GitHub Package Registry requires an extra authentication step (see https://github.community/t/docker-pull-from-public-github-package-registry-fail-with-no-basic-auth-credentials-error/16358 for ongoing discussion). In case GitHub fixes this and allows a simpler integration of Actions and Package Registry, I've left the (skipped) job in .github/workflows/main.yml.
• We use GitHub Actions' native caching action to cache pip dependencies and node modules for the following jobs: test, lint, deps, static-tests, static-pipeline.

Resolves #7001. You can see the latest runs with runtimes at the bottom of this PR, or in the Checks tab.

This won't yet be able to run on pypa/warehouse since the secret environment variables for Docker Hub haven't been set up in this repo, only in my fork. This now runs fine on pypa/warehouse.

[pavanagrawal123]

hey @callmecampos, this looks really good! I had #7881 open for this, but I didn't have much time recently to fix it up. This is a way better approach then I had going. I'm going to close #7881 in favor of this!

[callmecampos]

@di tested out and made the changes you requested

[webknjaz]

@callmecampos Most (if not all) of the jobs here can be collapsed into a nice matrix. Are there any reasons for not implementing this?

[webknjaz]

I think adding a cron schedule here would be nice too

[webknjaz]

This won't be necessary if you make a matrix...

[di]

Hey @webknjaz, @callmecampos was working on this as part of his internship which is now finished. Would you like to take over here?

[webknjaz]

@di ah, I didn't know. If he is not going to keep working on this PR, I'll try to find some time myself, but no promises.