Dependency Proxy

We are hoping to enable dependency proxy on .com soon. Please see https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8325 for the setup issue. The docs for this feature can be found at this location

@trizzi can you please help me fill this readiness review out and/or help me find any of the devs of this feature to help? Do keep in mind that every question may not be relevant in this case.