[Ingest pipelines] Deleting a special pipeline

[alisonelizabeth]

When you try to delete a pipeline that is mapped as the default_pipeline and or as final_pipeline in any index, regardless if rolled over or not. You cannot delete it, however the UI doesn’t tell you that. Would be nice:

• You can delete it, if the index template does not reference to this version anymore
• You can delete it, if there is no active write index using this anymore
• You should be informed in the delete:
  • Fix index template: abc, def, …
  • Rollover index: abc, def, …

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)