Propagate NotFound error returned by GetRepoPath
We are currently wrapping some of the errors returned by GetRepoPath, which makes them lose the gRPC NotFound code.
This leads to a gRPC error code of Unknown, which counts towards our error SLO, paging the on-call.
Example incident: gitlab-com/gl-infra/production#6320 (closed).
This patch removes the wrapping, ensuring the error code is propagated to the client, and accounted for appropriately in logs and metrics.