[views] Add template set to mapping envs

[roxblnfk]

We've added ENVs mapping into views component with #22

Need to add ability to define views scope for example using template_set key like this:

  # namespace:env_mappings
  - name: env_mappings
    kind: registry.entry
    meta:
      type: view.env_mapping
      category: my-module
      priority: 20
      template_set: namespace:templates
    mappings:
      env_name: env_id_or_name