Allow selecting multiple pictures in the Photo & Video Library attachment menu

### Your use case

#### What would you like to do?
In the previous Element app, it was possible to select multiple images to send in one go, this does not seem to be supported in Element X.

#### Why would you like to do it?
It is cumbersome to send each image one by one (or to send them all using Share from the Gallery app as described below).

#### How would you like to achieve it?
Make the Media Library selector support selecting multiple items. and pass them back to be sent in the message.

### Have you considered any alternatives?

It is possible to select many pictures in the Gallery app outside of Element, choose Share, select Element X for sharing, and then send them all in one go. But that is a workaround and not the most convenient solution.

### Additional context

_No response_

### Are you willing to provide a PR?

No

Start by tracing the Photo & Video Library attachment menu to the Media Library selector and follow how selected items are passed back for sending. Done means multiple pictures can be selected in one interaction and sent together in a single message.

Written by the indexing model from the issue text.