Add the option to display Public Rooms in dedicated tab

### Your use case

#### What would you like to do?
Display public rooms in a new dedicated tab to separate them from other private, encrypted conversations.

#### Why would you like to do it?
Public rooms can be quite "noisy", with a big number of members sending messages at a high frequency. This can result in a private message being hidden under a pile of public messages.
In addition to that, the separation would allow to make it more clear to the users that public rooms are not encrypted.
In Tchap we had to use specific icons and labels to mark public rooms, which FYI are called "Forums" in Tchap. Having a dedicated tab would make the UI way easier and cleaner.

#### How would you like to achieve it?
This can be an option available to the user in settings or to a developer like DINUM.

A new icon will have to be defined for this new tab. Here is a suggestion (bottom right of the screen)

### Have you considered any alternatives?

_No response_

### Additional context

_No response_