Adding a /.well-known/assetlinks.json file for android deeplink verification

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For apps targeting newer android versions, the playstore seems to require verification of domains to allow deeplinking.
If this is not happening, there is an error like shown here https://developer.android.com/training/app-links#manage-verify

Additionally they warn about this:

> Note: On Android 11 (API level 30) and lower, the system doesn't verify your app as a default handler unless it finds a matching Digital Asset Links file for all hosts that you define in the manifest.

https://developer.android.com/training/app-links/verify-android-applinks#multi-host

To verify an app, you need the app's fingerprint in a json. This is described within https://developer.android.com/training/app-links/verify-android-applinks#web-assoc

This page is somewhat a special case compared to what android intended, so it probably makes sense to have the json file within this repo so that the community is allowed to add their app.

It would be great if this can be somehow figured out. I assume this also may become relevant for the Element apps, since they might or will hit this issue too on newer android apps.

Start with the Android App Links verification documentation linked in the issue and inspect how this repository serves static paths. Determine the community app format and add /.well-known/assetlinks.json so listed apps can verify matrix.to; confirm the file is publicly served at that exact URL.

Written by the indexing model from the issue text.