Enable automated golden refresh

Currently, when we update our gapic-generator templates, we have to manually update the golden services. At the same time, we have an Integration test that will alert us if the goldens we generate differ from what's expected

We should use the logic we already have in that CI test, and add a step where the CI will push changes to our goldens when the templates are modified. This would save manual work, and be easier to communicate to new team members