Ref::FindAllBranchNames is occasionally returning `NotFound` status

~Conversation #220 (closed)

As part of https://gitlab.com/gitlab-com/infrastructure/issues/1951, the Ref::FindAllBranchNames endpoint was switched on.

We noticed a low rate of NotFound status responses being returned from Gitaly, but we unable to determine whether these error statuses were genuine or not.

These errors may be completely reasonable (the result of bad requests) but without evidence, we cannot yet turn it on in production.

Gitaly needs better logging for errors, so that we can determine what the cause of these errors is.