Add v2 OAuth to Gatekeeper
This new v2 OAuth is for the new OAuth flow from GitLab UI as described in https://docs.gitlab.com/ee/architecture/blueprints/observability_tracing/#authentication-and-authorization
This new v2 OAuth is for the new OAuth flow from GitLab UI as described in https://docs.gitlab.com/ee/architecture/blueprints/observability_tracing/#authentication-and-authorization