gitserver dhall component: break out internal/generate into kind pieces (statefulset, service and pvs)

Created by: uwedeportivo

the internal type is too hard to test right now. break it apart into subdirs and self-contained kind pieces (statefulset, service and pvs). this makes it more similar to what we will do with jaeger side-car.

use this refactoring to write tests that verify that customizations are applied correctly