Way to register "My Nextcloud" instance URL for better integration with app store

Home Assistant has an interesting concept of a permanent way to say which instance is "My Home Assistant". It can be set at https://my.home-assistant.io/

As per [their FAQ](https://my.home-assistant.io/faq/):
> This URL is only stored in your browser.

This then allows nice things like adding buttons to "Show app on my Home Assistant" which acts as a deeplink into your own instance.
See an example here, when you scroll a bit:
https://www.music-assistant.io/

This could be very useful for the detail pages at https://apps.nextcloud.com so it’s linked to your own instance.