Feature: locally merge HelmRelease values with flux binary

[lennartack]

It would be helpful if there was a way to locally merge values from ConfigMaps, Secrets and inline values into a single values.yaml. This would allow one to compare changes to in-cluster values using helm get values. It would also make it easier to manage HelmRelease via GitOps when one does not have access to all cluster resources and can't use helm get values.

#2808 requests a feature to build the full helm release, which apparently is hard to implement. But just building the values sounds easier.

If we get this feature it would also be nice if you can opt out of using values from Secrets.