Set Custom Image in Emoji Field

Is your feature request related to a problem? Please describe.
I really, really like the emoji-in-page-title design. It's fun, easy to use, and gives a little bit more visual distinction between different Collective Pages.

One thing that I would really like, though, is the ability to choose a custom image instead of an emoji. This could be really useful for internal knowledge bases that feature different organizations, products, or people, and offers a simple visual way to identify these things.

Describe the solution you'd like
Being able to either upload an image, or use something already in Nextcloud sounds like a pretty good approach to me.

Describe alternatives you've considered
Mastodon does this thing where admins can create custom emoji with unique images and shortcodes. Maybe we could just have a section to set that up, or maybe even depend on another addon for it?

Additional context
More than anything, this is kind of just a "nice to have" quality of life thing. Being able to associate logos to pages and then see them rendered in an embedded table or something could be really brilliant for those of us trying to run a tracker of a bunch of different projects or organizations.

No implementation files or tests are named. Start by locating the existing emoji-in-page-title entry point, then clarify whether the image source should be an upload, an existing Nextcloud image, or custom emoji; done should include displaying the chosen image wherever the page emoji currently appears, including embedded tables.