add emoji by URL, and/or copy an emoji originating from another instance

A feature that exist in GoToSocial is a "steal this look" option in the admin tool. If you like an emoji someone else is using, just find the link to the post with the emoji and it automatically pulls it in for you. via https://mastodon.social/@box464/112086707119143294

• [ ] copy emojis from a post/activity
• [ ] copy emojis from an instance (eg https://codeberg.org/tela/fedimoji)

Related issue: https://github.com/bonfire-networks/bonfire-app/issues/909

Relevant code:

• Upload of custom emoji: https://github.com/bonfire-networks/bonfire_files/blob/main/lib/web/upload_emoji_live.ex
• inclusion of custom emojis in text: https://github.com/bonfire-networks/bonfire_common/blob/main/lib/text.ex#L559 and https://github.com/bonfire-networks/emote/blob/master/lib/emote.ex