fix: ignore ResourceExhausted grpc code

What

Ignore the ResourceExhausted grpc code returned by ratelimiter in gitaly from error rate calculation.

Why

Rate limiter in gitaly was returning Unvailable grpc code until now, and a fix has been pushed in gitlab-org/gitaly!5084 (merged) to return ResourceExhausted grpc code, which signifies that the user has attempted to access resources too fast too quickly and hence it's a user error rather than a server-side error and therefore it should be excluded from error rate calculations.

Reference issue: https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16844