Ability to set an explicit order for Favourites.

### Steps to reproduce

1. View the Favourites section (once we have sections again)
2. Expect to see your favourites in a consistent order, so you can use muscle memory to jump to them
3. Discover that because favs are typically ordered by activity, you can't use muscle memory.

### Outcome

#### What did you expect?

Back when we first implemented favourites, you could order them by drop & drag in a specific order so you could use muscle memory to always find the right ones. This got deleted at some point. Perhaps we can have it back when we reintroduce the favs section?

#### What happened instead?

No muscle memory.

An alternative approach could be to pin rooms like you can on iMessage now.

### Operating system

_No response_

### Application version

_No response_

### How did you install the app?

_No response_

### Homeserver

_No response_

### Will you send logs?

No