Enable feature flag for go update hooks through operations service

Enables ruby gitaly feature flag to enable the go update hook. Also updates the operations service tests to test with the feature flags more easily.

in !2095 (merged), we enabled the go feature flag and it has been turned on in gitlab.com without issue.

https://dashboards.gitlab.net/d/000000199/gitaly-feature-status?orgId=1&refresh=5m&var-environment=gprd&var-method=UpdateHook&var-prometheus=prometheus-01-inf-gprd&from=now-24h&to=now