Allow sentence metadata in responses

[synesthesiam]

Sentence metadata was added to hassil in version 1.6.0:

language: en
intents:
  TestIntent:
    data:
      - sentences:
        - "..."
        metadata:
          key: value
        response: test_response

This PR exposes that metadata to response rendering as a metadata object:

language: en
responses:
  intents:
    TestIntent:
      test_response: "{{ metadata.key }}" 

This allows sentence authors to pass language-specific data to response templates, such as the non-inflected/base forms of nouns that are part of the matched sentence (device class, etc.).

[synesthesiam]

@witold-gren Can you try this out and let me know if it works for you? I still need to modify Home Assistant core for this to work in Assist, but I want to make sure it's correct here first.

[witold-gren]

I can confirm that now it works properly on intents scripts (this repository). Thanks for this improvement @synesthesiam

[tetele]

Appologies for the delay. Simple, but very useful contribution, this <3