Source code endpoint thresholds

What does this MR do and why?

Add endpoint threshold changes for groupsource code as described in this comment

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.

Closes https://gitlab.com/gitlab-com/create-stage/create-engineering-managers/-/issues/368

Related to gitlab-com/gl-infra/scalability#1315 (closed)