Spinnaker-Backend - Remove pipeline from Spinnaker give a name change - planning

Give a name change, pipelines will remain orphaned in an application.
This could cause confusion or worse, a trigger of the wrong pipeline may produce inconsistent application states in prod.

To mitigate these problems we must be able to remove unused pipelines during the `save` command.

Plan out the implications of such a "fix" and a mitigation for the possible errors.

Start by locating the save command and the Spinnaker pipeline handling in the repository. Trace how application name changes leave pipelines orphaned, then document the implications, failure cases, and a mitigation plan; done means the plan clearly defines safe removal behavior and error handling.

Written by the indexing model from the issue text.