Allow emoji reactions for notifications (esp. user joins room)

[andrewtavis]

Hi there :)

Started using Element over the last week and am really enjoying it, so firstly thank you!

A basic thing that I'd assume to be able to do and can't is to react to the notification that someone joined the room. It would be nice to be able to do a small gesture to welcome people. I'd say other notifications would also be situations where reactions might be useful, like say the one where someone is made a moderator where people could congratulate them (or thumbs down it, who knows 😅).

I'm on web and iOS, as far as platforms are concerned. I looked in the element-web issues and there wasn't anything explicit for this that I could find (just one on Discordification where this could be mentioned). I'm happy to open an issue if there'd be interest, but wanted to check here first 😊

Thanks again!