Backend/Frontend: Add new `previousStagesJobs` field to combine with `needs` field.

Summary

Currently, the builds page (See example here) and the show pipelines page (See example here) take an extraordinarily long time to load (between 9-13sec) when there is a significant amount of data that is needing to be shown in the pipeline. This makes it extremely difficult to work with and review from a user perspective when attempting to pinpoint a problem that needs attention quickly.

Proposal

On the backend, create new previousStageJobs which returns all the jobs of a previous stage. On the frontend, this will be combined with needs field to replace previousStageJobsOrNeeds field.

Additional details

Some relevant technical details, if applicable, such as:

• Does this need a feature flag?
• Is there an example response showing the data structure that should be returned (new endpoints only)?
• What permissions should be used?
• Is this EE or CE?
  • EE
  • CE
• Additional comments:

Implementation Table

Group	Issue Link
backend	Backend: Fix N+1 in previousStageJobs (#424255 - closed)
backend	👈 You are here
backend	Backend: Fix N+1 in previousStageJobsAndNeeds (#422079 - closed)
backend	Backend: Remove GraphQL field - previousStageJo... (#424417)

Links/References