Set a default for add-on options and schema config

[frenck]

Proposed change

It is always nice if an add-on doesn't need any options (and thus might not have a schema).

This PR adds a default empty dictionaries to the schema and options configuration parameters of an add-on configuration, mainly for cleaner add-on configurations.

For a future improvement, it would be nice if we could expose if the add-on has options (and thus a schema) and hide the config from the UI based on that.

Type of change

• Document existing features within Home Assistant
• Document new or changing features which there is an existing pull request elsewhere
• Spelling or grammatical corrections, or rewording for improved clarity
• Changes to the backend of this documentation
• Removed stale or deprecated documentation

Additional information

• This PR fixes or closes issue: fixes #
• Link to relevant existing code or pull request: Set a default for add-on options and schema config supervisor#2421

[ludeeus]

home-assistant/frontend#8130 for the frontend part.

[ludeeus]

✔️ Can be merged when the parent PR is merged.