Allow mobile apps to provide QR code functionality

[balloob]

Breaking change

Proposed change

This adds a new QR Code scanner feature to the external bus. Goal is that mobile apps will display this UI and return the scan result back to Home Assistant.

If alternative option label is not given, that link will not be shown to the user.

This PR is step 1. Next step is to ask Android/iOS to add support for this.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

[bramkragten]

Should we also tell the app what kind of QR codes we want to scan, what to accept, or does the app give the frontend everything it finds, and we tell it if that is something we accept/scan, so if we are done and it can remove the scanner?

I'm thinking about 2 QR codes side by side on a package, you dont want the app to give the wrong code to the frontend.

[balloob]

I think we can start with accepting everything. We can expand it later to limit the things it accept. I would love for the frontend to get a generic QR code scanner that could work with a new concept of QR discovery for manifest.json.