Enable the gitlab-http gem

What does this MR do and why?

Related to #426549 (closed)

This MR enables the feature flag use_gitlab_http_v2.

It's working on SaaS stable since Nov 1, 2023. #426549 (comment 1629562570)

Normally, we could remove the feature flag and let the new code stay but I think this is safer for self-hosted users in case they have unexpected configs. Ref: omnibus-gitlab#8277 (closed), gitlab-org/build/CNG!1557 (merged)

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