Allow changing homeserver details without logging out

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There are multiple scenarios:

• Server migrates its delegated domain
• Server migrates from not using delegation to moving it
• Some configuration error in .well-known and proxy lead to wrong URLs which have been patched, but also that means the server has "moved"

I had to go through these, with a userbase larger than Me, Myself, and I.
From my experience, once you're logged into Element, the homeserver as either set or discovered on login, is saved and set in stone.

That means, your users need to re-log, re-sync, maybe use their e2e keys if not done correctly.

This could all be circumvented if the homeserver setting could be changed manually or "rediscovered".

I am not sure what security risk allowing to chang your homesever might open. Perhaps it is enough mitigation to only allow (sub) domains of the server part of your MXID.

It could also be rediscovered by reading the .well-known/matrix/client again, which should also be fairly secure, since again it's hosted on the domain that owns my server, as bound to my MXID.