Make expanded commit diff files rate limit configurable via application settings

Context

Make https://docs.gitlab.com/ee/security/rate_limits.html#commit-diff-files rate limit configurable via application settings.

The Gitlab Performance Tool is used to test endpoint performance under load, and disables application rate limits to do so. If a rate limit is not configurable it might be disruptive for customers. Some additional context where a similar rate limit ran into some issues is here: https://gitlab.com/gitlab-org/quality/quality-engineering/team-tasks/-/issues/3253#note_2256131160