Sort Activity options

### Your use case

#### What would you like to do?

Sort Activity - I'm not really sure what defines "Activity" but I am sure it isn't what I personally want.

What I personally want:
When I post, or when someone replies to me, that moves the room to the top of the list.

Here is what I am talking about in case it isn't obvious

#### Why would you like to do it?

To make it easier to monitor rooms I am mostest interested in.

#### How would you like to achieve it?
Wait patiently for someone to implement it :)

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

No implementation file, entry point, or test is named in the issue. Start by locating the room-list sorting and Activity ordering code in the relevant Element client, then compare the current behavior with the requested rule: rooms move up when the user posts or someone replies to them. Done means the sorting option is available and covered by tests for both activity cases.

Written by the indexing model from the issue text.