Add mutation to promote timeline event from a note

What does this MR do and why?

Contributes to #344058 (closed)

Adds a GraphQL mutation to promote a timeline event from a note.

---

I've considered two different solutions here.

One is to extend and reuse an existing GraphQL Mutation for creating timeline events (CreateTimelineEvent) introduced in !78884 (merged).

Another (current) is to have a separate mutation to promote a comment to a timeline event.

To reuse the existing CreateTimelineEvent mutation, we would need to modify it to accept two different input sets:

• With provided incident_id, note, and occured_at. With blank promoted_from_note_id.
• With provided promoted_from_note_id. With blank (or ignored) incident_id, note, and occured_at.

I found the approach, with a separate migration, simpler and less confusing. With that approach, we would have two migrations. Each of them will be responsible for their only job.

Screenshots or screen recordings

Before	Mutation	After

GraphQL Mutation

Mutation

mutation PromoteTimelineEvent($input: TimelineEventPromoteFromNoteInput!) {
  timelineEventPromoteFromNote(input: $input) {
    timelineEvent {
      id
      author { id username }
      updatedByUser { id username }
      incident { id title }
      note
      noteHtml
      promotedFromNote { id body }
      editable
      action
      occurredAt
      createdAt
      updatedAt
    }
    errors
  }
}

Query variables

{
  "input": {
  	"noteId": "gid://gitlab/Note/1404"
  }
}

How to set up and validate locally

• Navigate to Monitor > Incidents from the left sidebar menu of your GitLab project
• Create a new incident
• Create a new comment on the incident's page
• Grab the last comment ID
  • Call Note.last.id from bundle exec rails c
  • Or by inspecting HTML source of the page and find li tag with id id="note_<id>"
• Open http://localhost:3000/-/graphql-explorer
• Copy & Paste mutation example
• Copy & Paste mutation query variables and update note ID with the note ID from the previous steps
• Run the mutations in GraphiQL
• Check IncidentManagement::TimelineEvent.find(<TimeLineID>) in the rails console

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.