Convert animated stickers even when media_patterns.stickers is set

[dongcarl]

When media_patterns.stickers is set, animated stickers (lottie) are not converted and the message directs clients to fetch it from the corresponding mxc:// URL. This is problematic for clients that can't interpret lottie animations.

There should be some setting that allows for certain sticker types (e.g. lottie, but not others) to still be converted and served by the local homeserver even when media_patterns.stickers is set.