Propagate Gitaly LimitError to client

One cause of production incidents is when a surge of traffic can land in Gitaly where it tries to serve the requests. However, some of these requests end up needing resource intensive operations. https://gitlab.com/gitlab-com/gl-infra/production/-/issues/6172 is an example.

To prevent Gitaly from falling over in these scenarios, the producer of the traffic ought to be notified and limited. Gitaly already has this capability through rate limiting and concurrency limiting. Gitaly will return an error message when requests hit a certain limit. This way, Gitaly won't enter into a resource exhaustion failure mode.

This error message is protobuf message defined by gitaly!4476 (merged).

Once gitlab-shell receives this error, it needs to propagate this error in a helpful way to the client.

What we want is to fail with an error like this:

> git clone ssh://git@127.0.0.1:2222/gitlab-org/gitlab.git
Cloning into 'gitlab'...
error: too many requests
>