Implement Helm template handler for Helm storage backend

Description

Implement the storage backend that supports helm templating:

Implement as a part of the same binary of the Helm release storage (cmd/helm-storage-backend)
Create dedicated Type for a given Storage backend TypeInstance
- In context: go template + helm release name + namespace
Implement templating support:
- Template passed in context to the storage backend - it is specified and stored in Local Hub on create/update
- The service renders the template against the manifests and values for the installed release, and returns the output
- (Almost) the same logic that we have currently in Helm Runner

See epic #650