Add `discussions` field to `PipelineSecurityReportFinding`

Why are we doing this work

In order to migrate the pipeline security tab to GraphQL we need to add a discussions field to the PipelineSecurityReportFinding type.

This should be the same as on the Vulnerability type (extending the NoteableInterface):

discussions(
  after: String
  before: String
  first: Int
  last: Int
): DiscussionConnection!

This should allow us to use the following mutations:

• createNote
• destroyNote
• updateNote

Potential Issue: all the mutations listed above expect a Global ID of the note to update. But PipelineSecurityReportFinding currently does not have a global ID, but only a uuid.

Relevant links

Non-functional requirements

• Documentation: Update GraphQL docs
• Testing: Add test

Implementation plan

• backend Add a discussions field to the PipelineSecurityReportFinding type.
  • This should be the same as on the Vulnerability type (extending the NoteableInterface)

Verification steps

• Corresponding test coverage to be reviewed by counterpart SET