Bubbles should not show sender when in a chat with one other

### Your use case

#### What would you like to do?
Not show the name of the person you are in a conversation with above every bubble when the private chat only has one other person in it (I.E. a direct message conversation).

#### Why would you like to do it?
It's very cluttered to always see the name when you already know who it is.

#### How would you like to achieve it?
Removal of name when in direct messages (1 on 1 chats). This is also applicable to other clients including web, but I will post here for starters.

### Have you considered any alternatives?

There are no easy alternatives.

### Additional context

This is especially beneficial when bridging other private chat services, such as Signal, if you wish to use Element as a replacement UI.

### Are you willing to provide a PR?

Yes