Add gitlab.gitaly_disable_request_limits config variable

What does this Merge Request do and why?

The GITALY_DISABLE_REQUEST_LIMITS environment variable can be used to disable a development-only check to find Gitaly N+1 queries. However, the request limit check often times it gets in the way of development--particularly in Sidekiq--since it might be flagging existing issues that disappear when the cache is populated.

We now add a config option to disable this limit checking.

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.