Handle structured errors for Gitaly Blame RPC

Problem

We had a bug related to blame functionality: GRPC::Internal: 13:streaming raw blame data: ex... (#425013 - closed).

After change to Gitaly code, the blame RPC started returning GRPC::Internal error if user requested a blame range out of range.

It was temporary fixed by adding an handle for GRCP::Internal error: !131638 (merged)

Solution

Gitaly provides structured errors format for blame related errors now: gitaly!6361 (merged)

We should remove a handle for global GRPC::Internal error and catch structured errors instead.