Pipeline connections are not / can not be deleted via API

[bdkuhman]

Expected Behavior

Pipeline connections are deleted/removed after deleting a pipeline or stream

Current Behavior

After deleting a stream or pipeline, Entries remain in the connections
Attempting to modify a connection through the API results in "Stream <> not found!" or "No pipeline with id " responses.

Possible Solution

a DELETE endpoint /system/pipelines/connections/<connection_id> to be able to clear out an empty stream ID
When a pipeline is deleted, the pipeline is cleared from all stream connections
When a stream is deleted, it is removed from the connections

Steps to Reproduce (for bugs)

1. Create a Stream
2. Create a pipeline
3. Connect stream to pipeline
4. Delete Stream, or Pipeline
5. Response data from GET /system/pipelines/connections still contains data for deleted stream/pipeline

Context

I was playing around with the API, and noticed this behavior when trying to write a script to automate some tasks, that connections stick around.

Your Environment

• Graylog Version: 5.2.6/6.0.4
• Java Version:
• OpenSearch Version:
• MongoDB Version:
• Operating System:
• Browser version:

[tellistone]

Note: not reflected in the UI, specific to API