Github actions and workflows fine tuning

[kdave]

Tracking issue for various gh actions tuning.

• Actions status: https://github.com/kdave/btrfs-progs/actions
• Documentation: https://docs.github.com/en/actions

[kdave]

Basic coverage is in devel. Further work:

• [x] add workflow for release, triggered by pushing branch release-test
  • [x] run build tests in docker containers
  • run tests/build-tests.sh in Tumbleweed container that supports all build targets
• add maybe more workflows branching from checkout to functional and build-only tests
• add template for self-hosted runners
• [x] add workflow for pull requests with basic build checks
• [x] extend test matrix to build with clang too

[kdave]

https://github.com/actions/runner-images image details, updates, package versions

[kdave]

https://dev.to/dtinth/caching-docker-builds-in-github-actions-which-approach-is-the-fastest-a-research-18ei possible ways how to cache docker images (2020)

[kdave]

Skip testing when only documentation changes are pushed (Documentation/*.rst). https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#running-your-workflow-only-when-a-push-affects-specific-files

[kdave]

Documentation-only patches can use the [ci skip] directive, no automation around that is needed. What works now is sufficient: devel, ci/* branches, pull requests, gcc, clang, distro coverage.