Adding message search to default search bar

### Your use case

#### What would you like to do?
Search all room messages with the default command-k / top-left search.
#### Why would you like to do it?
Messages are by and large the most common thing that I'd like to search and the current search mechanism is painful - requires multiple clicks and is not at all intuitive.
#### How would you like to achieve it?
Currently the search feature, at the bottom, has a "Search for:" Public spaces, Public rooms, People. I'd like to add a "messages" option to that at the bottom, which has the exact same UI as the standard message search UI but within the searchbox. I'm also happy to bring the user to the All-room message search when they click the button.

### Have you considered any alternatives?

_No response_

### Additional context

The org I work for uses Element as our primary comms platform and would be excited to put a few-hundred-dollar bounty on getting this feature this week if that's something that would be amenable.

I'd also be very very happy to submit the second version of this as a PR myself.