Option to not push registration "prompts" to users

### Your use case

#### What would you like to do?
As we are ultimately want to replace Jitsi with Element Call stand alone, I'd like to have an config option so that EC would not suggest registration "every other time" an user is doing anything in our EC web page.

Registration can still be available and so on just like it is now, but EC shouldn't push advertising it all the time.. So an config option to tame / disable "registration suggestions" would be awesome.

### Have you considered any alternatives?

N/A

### Additional context

N/A