LLM completion to resolve vulnerability from MR

There currently exists a completion to resolve a vulnerability. The scope of this issue is either adapt the existing completion or create a new one to make it possible to resolve a vulnerability in the context of a merge request. The different inputs in this case would be:

• the vulnerability finding instance related to the latest MR pipeline run
• the related code in the MR branch

This functionality would likely be built on the interface created as part of #480773 (closed)

Implementation plan:

!164555 (diffs) this is from the spike