Implement endpoint to perform request to services running in builds

Merged Francisco Javier López requested to merge fj-5276-mirror-webide-changes into master

What does this MR do?

In order to implement https://gitlab.com/gitlab-org/gitlab-ee/issues/5276 we need several modifications and this is one of them.

In this MR:

  • add a new endpoint to proxy websocket requests
  • extend the JobsController controller to handle the proxy request calls
  • add the feature flag build_service_proxy to allow/disallow service proxy connections

What are the relevant issue numbers?

Refs https://gitlab.com/gitlab-org/gitlab-ee/issues/5276 and closes https://gitlab.com/gitlab-org/gitlab-ee/issues/9538

Does this MR meet the acceptance criteria?

Edited by Francisco Javier López