Custom emoji BE and API
Custom emoji BE and API to support the designs in #48907.
When this issue is finished, you should be able to add/remove emoji to the database. But you won't be able to do anything in the Web UI. And you won't even see them as they won't be useable in the Web UI.
The order of the custom emoji feature is in &292.
After this is implemented, we will document that the BE API is available, but it is essentially not useful, and point to the epic as an explanation of why we are doing this.