Message batching

[rsimon]

Right now, the Supabase plugin pretty much fires out a realtime message for every store update. For image annotations, this can lead to a high number of updates (when dragging a shape). By design, the Supabase SDK discards messages after a given threshold. This typically leads to the following situation:

• User drags a shape
• Drag gets synchronized to other users until message rate threshold is reached
• Synchronization stops for other users
• Once the user deselects the shape and thus commits the change to the DB, other users will see a small jump as the final state is re-established

This is a cosmetic issue more than anything else. But ideally, we'd want a message batching mechanism, which debounces thje store updates and only sends a controlled number of broadcast messages. This would avoid the final jump, as the DB change data capture message re-establishes "true" sync.