Image edits from Telegram are not handled correctly

[tulir]

Official clients probably don't support it, but it's possible.

[JuniorJPDJ]

It's pretty common now to edit already sent images. Would be cool to have it fixed. Thanks for your development ;D

[tulir]

Image edits should work now since I changed the bridge to store the image event ID instead of the caption event ID. It means edited captions won't work, but that's hopefully less problematic.

There's also a config option to send the caption as the body as per MSC2530, which makes everything work correctly, but clients don't really support it yet.