Refactor concept of "AuthProviders"

[fnwbr]

What used to be "authentication providers" are now rather "application" or "service" providers.
Initially we had assumed that every page or service would have their own authentication layer, which was true in case case of Etherpads/MyPads and Spacedeck.

Now with ditching Spacedeck in favor of tldraw one of those services is gone.

Right now I'm not sure what a better solution would look like; but something along the lines of:

1. Matrix is the primary authentication layer and major entry point
2. We have "apps", "services" or "applications" such as etherpad, tldraw or something else.
   2.1. Each of those can provide an additional authentication layer, like in the case of Etherpad specifying MyPads
3. Generally each "application" stores their respective data in a sub-space of the "Applications" Matrix space
4. Each "application" can provide a custom path for routing / custom name for whitelabeling (e.g. calling the tldraw app /draw or the etherpad app /note)