Play GIFs only when Element is the active window

### Your use case

#### What would you like to do?
I would like GIFs to autoplay, but only when Element is the active window.

#### Why would you like to do it?
Currently the only options are:
* Always play GIFs (But this can be distracting if I'm focussed on another window.)
* Hover to play GIFs (But I don't want viewing a GIF to prevent me from moving my mouse to other parts of the UI or the message box.)

#### How would you like to achieve it?
I think the "Autoplay GIFs and videos" should become a setting with multiple states instead of a toggle.

* Only when hovered over the GIF (equivalent of having "Autoplay GIFs and videos" off)
* Only when Element is the active window
* Always (equivalent of having "Autoplay GIFs and videos" on)

### Have you considered any alternatives?

_No response_

### Additional context

I have tested the behavior on other platforms as well to check what they do.

* Discord has the requested behavior by default
* Slack always autoplays GIFs
* Rocket.Chat always autoplays GIFs