Deprecate matrix.to for FediLinks

[SoniEx2]

The Fedi Links project is a project to introduce URI fallbacks in spite of OS/browser/client support. The main specification for the fallback behaviour is https://fedilinks.org/2 .

It would be neat to deprecate matrix.to entirely, tho we recognize that's a few years off. A good start would be to decide on what a hypothetical web+matrix URI should look like. Ideally, a web+matrix URI fallback would support viewing public rooms as a guest if the server allows for it, directly on the home server. This would help bridge the world of matrix with the world of the web.

Plus, what happens if the project dies/runs out of funding/gets bought out? A native fallback cannot be controlled, while matrix.to can be killed. Deprecating matrix.to would help with the bus factor.