Fix N+1 in projects REST endpoint and forked projects

What does this MR do?

When retrieve projects from the /projects REST endpoint and there are several forked projects, some N+1 are present. In this MR we fix the N+1 in the namespace, project_features, and users field of forked projects.

Before the MR, the namespace for forked projects behaved like this:

With the preload of that relation, the new query is:

The project_features relation also behaved badly formerly:

With the preload:

Lastly, the users also presented an N+1 when trying to render the avatar url:

But now with the preload:

Does this MR meet the acceptance criteria?

Conformity

• Does this MR need a changelog?
  • I have included a changelog entry.
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Related to #21121 (closed)

changed milestone to %13.11

added backend bugperformance database groupeditor [DEPRECATED] priority4 querylimiting-disable severity4 workflowin dev labels

added 1 commit

• 8b925277 - Fix N+1 in projects REST endpoint and forked projects

Compare with previous version

added databasereview pending label

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Category	Reviewer	Maintainer
backend	Terri Chu (@terrichu) (UTC-4, 6 hours behind @fjsanpedro)	Mikołaj Wawrzyniak (@mikolaj_wawrzyniak) (UTC+2, same timezone as @fjsanpedro)
database	Mehmet Emin Inac (@minac) (UTC+2, same timezone as @fjsanpedro)	Tiger Watson (@tigerwnz) (UTC+13, 11 hours ahead of @fjsanpedro)

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Generated by Danger

marked the checklist item I have included a changelog entry. as completed

marked the checklist item Code review guidelines as completed

marked the checklist item Merge request performance guidelines as completed

marked the checklist item Database guides as completed

marked the checklist item Style guides as completed

marked the checklist item Separation of EE specific content as completed

@terrichu can you review the BE part of this MR? @alexives can you review the database part of this MR?

requested review from @terrichu

requested review from @alexives

removed review request for @alexives

requested review from @alexives

approved this merge request

added databasereviewed label and removed databasereview pending label