Improve message and behaviour in federated rooms with dirty Talk-Hash

Something for later, but this should say something like:
> "Nextcloud Talk was updated on the federated server."

And we should have a look if we can make sure it does not yield when you open such a conversation the first time

_Originally posted by @nickvergessen in https://github.com/nextcloud/spreed/pull/14181#discussion_r1927188029_
            