Backend: Batch request calls to Gitaly when fetching `include`

Summary

Currently, we allow 100 includes and each include triggers a Gitaly call. Our docs recommend not going over 30 Gitaly calls per request: https://docs.gitlab.com/ee/development/gitaly.html#toomanyinvocationserror-errors

Proposal

These requests to Gitaly should be batched

Useful data here: &7290 (comment 1168994718) <- Internal only

Implementation

Work Type	Description	Issue link
	NOTE: 🚨 All below issues can be done in parallel
backend	Backend: The gitlab-ci.yml is limited to 100 includes	#207270 (closed)
backend	Backend: Remove N+1 for Gitaly requests when fetching includes	#344829 (closed)
backend frontend	Improve the error messaging when fetching remote includes are timing out	#351168 (closed)
backend	Backend: Improve CI Linter performance through parallelizing HTTP calls	#351250 (closed)
backend	Backend: Caching includes to improve performance when using remote includes	#351252
backend	Backend: Batch request calls to Gitaly when fetching include	👈 You are here
backend	Backend: Group files by projects in config_file_project_validate_access	#382751 (closed)