Shortcut to view all new messages (like irssi alt-a)

### Your use case

#### What would you like to do?
Irssi, WeeChat and other oldschool IRC clients have a hotkey that can be pressed and the client
jumps to channel with most important messages. Element has shift-alt-down which does almost
the same but not properly and is limited to selected space.

#### Why would you like to it?
It's just super quick way to read all your relevant messages by hitting same key all over again. No mouse needed.

#### How would you like to achieve it?
1) Define hotkey. alt-a is the "standard", not sure if it can be used in browser/electron. Any combo that can be pressed with one hand easily is ok.
2) Define algorithm how to prioritize which room to show. I'd suggest algorithm: 1) Room with largest number of mentions 2) Favorited room with largest number of unread lines 3) Non-lowpriority-room with largest number of unread lines 4) Nothing (Ignore low priority rooms and joins/parts).

#3232 is related.

### Have you considered any alternatives?

Not really.

### Additional context

_No response_