Document new addon config folder options

[mdegat01]

Proposed change

Document new options added for config collection from users in addons added in home-assistant/supervisor#4650

Also put a blurb explaining how and why an addon developer might use this new feature.

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: Add dedicated add-on config folder supervisor#4650