Better documentation for GitHub Actions and `CODEOWNERS`

[justaugustus]

From https://github.com/pauldoomgov/.allstar?tab=readme-ov-file#unimplemented-checks:

We aren't using the policies for "Github Actions" (actions.yaml) or "CODEOWNERS" (codeowners.yaml) because they're not well-enough documented upstream for us to effectively deploy them.

cc: @pauldoomgov @pburkholder

[SunderSingh27]

I'm solving this issue #726