Draft: Add tombstone delete

Summary

Small changes to enable Cordra tombstone-delete, as well as some fixes and minimal cleanup of error messages.

This was tested against the GWDG Cordra instance and not the testbed. Set to draft because it does not pass the Pipeline.

Check List for the Author

• All automated tests pass
• Reference related issues
• Appropriate user and developer documentation for new code
• Annotations in code (Gitlab comments)

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Appropriate user and developer documentation for new code
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.