RPC service to list a subset of refs by name

Ci::Pipeline#latest? is making a Gitaly call to find the latest commit for a git_ref:

def latest?
  return false unless git_ref && commit.present?

  project.commit(git_ref) == commit
end

!1365 (merged) was supposed to help us reduce the number of RPC calls by batching the requests into a single one, but the response doesn't include any ref information, so we don't know how to match the returned commits with the refs.

gitlab#19697 (comment 324284522) proposes a new RefService RPC to get a list of refs by name and each returning ref should have a commit ID.

We already have Gitaly::FindAllBranchesRequest and Gitaly::FindAllTagNamesRequest but they return data for all refs from a project.