ci: streamline CI actions to prepare for merge queue introduction

[rami3l]

This is one of the prerequisites for closing #3567.

Changes

• Merge all *-on-*.yaml into ci.yaml.
• Merge all-features into ci.yaml.
• Merge test-docs into ci.yaml.
• Add freebsd-builds to ci.yaml.
  • Disassemble and reorganize ci/cirrus-templates.
• Add conclusion to ci.yaml.
• Make the CI fail if the generated ci.yaml is not up to date.

[rami3l]

This file is generated by the script, please ignore it while reviewing.

PS: Actually, it's probably better to ignore .github/workflows/** changes entirely.

[djc]

Yeah, I think that makes sense. Thanks for working through this!

[rami3l]

@djc Concern: If I'm not mistaken, the conditional if: ${{ (github.event.push && github.ref_name == 'master') || github.event.schedule }} doesn't seem to work (returns false on the latest master push), and it unfortunately hasn't been tested on PR.

The conditional is necessary since we want the workflow to always run to qualify for being used in branch protection.

What could've happened?

PS: This should not influence the future merge queue integration though, since it depends on a separate merge_group case.

[rami3l]

... I checked the docs again and I don't see why, but probably we should use github.event_name == 'push' instead of github.event.push?