Describe the request

So as I wrote in #468, pasting images is a nice feature. #413 (As It Obviously Turns Out) adds that, so I installed nightly flatpak to try it out. And IMHO, pressing Ctrl+V on the "Text" tab when an image is in the clipboard should go to the Image tab and do the paste there. Telegram for Android behaves exactly like this if you paste an image to it. Mastodon and Firefish (both of backends I've tried) do not require you to open the embed menu to paste an image either. Reddit, no matter how bad it is, just puts the image there if you Ctrl-V an image into the Text post. You name it.

Implementation Details

• This should be an option in settings.
• This should be only available to some fediverse backends. (Include which ones on the above field).
• This is client-only (and shouldn't sync with the instance).
• This follows the GNOME HIG.