Option/toggle to allow saving all room decrypted media to phone's shared storage, with previous user consent

### Your use case

#### What would you like to do?
Allow the user to automatically save downloaded decrypted pictures/media of specific rooms to phone the shared storage (for example to see all old pictures on the phone's gallery).
Previously warning the user that anyone having acces to the phone storage will we able to see this content.

#### Why would you like to do it?
To save and have fast access to all content locally on the phone without needing to scroll for months on the Element app chat.

#### How would you like to achieve it?
Having an option/toggle on the room/chat to allow saving decrypted media on shared phone storage.

### Have you considered any alternatives?

The built in room 'Uploads' > 'Media' works but it does not have access to old files (unless the user scrolls the room for old media, which is not practical if the media is not recent).

### Additional context

_No response_

### Are you willing to provide a PR?

No