Implement Helm template handler for Helm storage backend

[pkosiec]

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

Related issues

See epic #650