CommitService: implement ListCommits

This is a new method in Gitaly protocol 14.2. Quoting:

  // ListCommits lists all commits reachable via a set of references by doing a
  // graph walk. This deprecates ListNewCommits, FindAllCommits, FindCommits
  // (except Follow is not yet supported) and CommitsBetweenRequest. Any
  // unknown revisions will cause the RPC to fail.

It is necessary for hgitaly_repository_spec to pass on GitLab 14.2, and is called according to the between_uses_list_commits feature flag, which seems to be activated by default in HDK and CI, but not in production.

From GitLab::Git::Commit:

          wrapped_gitaly_errors do
            if Feature.enabled?(:between_uses_list_commits, default_enabled: :yaml)
              revisions = [head, "^#{base}"] # base..head

              repo.gitaly_commit_client.list_commits(revisions, reverse: true)
            else
              repo.gitaly_commit_client.between(base, head)
            end
          end
        end

This examples indicates that smart translation in revset at the level of genericity of ListCommits is a potential source of problems.