repository: Wait acknowledgement for CreateBundleFromRefList

CreateBundleFromRefList immediately starts streaming the data without waiting for acknowledgement. In the epic there are two issues described as a result:

1. This can cause hard to debug errors when an RPC is rejected due to for example a repository not existing.
2. This will become a bigger issue with &8971 (closed) as this prevents client-side retries of writes. The client can't retry the request on another node if it already started streaming the data to the other node without buffering the data.

I guess the changes in this MR will help with the first issue but will it really help with the second issue considering that the usage of this RPC is Gitaly internal? And seems like once we are in CreateBundle, we already have the all the data, we don't receive the stream itself from external client?

Closes #6229 (closed)