chore: Improve service owner tests and add deletion jobs

[marikaner]

Context

This PR does the same as SAP/ai-sdk-js#1676 only for Java.

This improves the test setup as follows:

• security

  • service owners will now be added directly to a sub team with write access to the repo
  • secure important workflows with auth check, so that only maintainers can call those workflows

• branch deletion

  • branches under spec-update are deleted automatically after 90 days
  • branch deletion on service owner side triggers branch deletion for the according branch directly
  • we could change this to run on a branch instead of file + file_ref which seems a little weird to me

• refactoring

  • file and file-ref were renamed to service and ref

I did not apply the "auth check" to any jobs. It is up to you if you want to use this and where.