GET /api/:version/repos/:namespace/:project/commits/:sha frequent Gitaly timeouts with GRPC::DeadlineExceeded: 4:Deadline Exceeded.

We see frequent Gitaly timeouts during Jira integration syncs.

The timeout happens in the Gitaly CommitDiff RPC call. Affected URIs will look like api/v3/repos/....

https://sentry.gitlab.net/gitlab/gitlabcom/issues/2646494/

GRPC::DeadlineExceeded: 4:Deadline Exceeded.
  grpc/generic/active_call.rb:29:in `check_status'
    fail GRPC::BadStatus.new_status_exception(
  grpc/generic/active_call.rb:180:in `attach_status_results_and_complete_call'
    recv_status_batch_result.check_status
  grpc/generic/active_call.rb:169:in `receive_and_check_status'
    attach_status_results_and_complete_call(batch_result)
  grpc/generic/active_call.rb:337:in `each_remote_read_then_finish'
    receive_and_check_status