Make constraint template maintainace easier at scale

[JaydipGabani]

No simple way to embed Rego policy at scale into the constraint template. User may want Rego files separate to maintain unit tests.

Couple of ideas -

1. Use helm function to compile constraint template via helm template, add example how to do this in the docs if possible.
2. gator compile command to copile CT from different files - from tmpl, rego, schema files