Now that `pinned_count` is stored in the database, we want to trigger an update when a message is pinned or unpinned to reflect the most up to date value of how many pins are in a thread. I chose to do this in `message-creator` because I thought it made the most sense to handle this when the pin message is created, and to update pinned_count in the same area where replies_count is updated since they are similar. However, I don't feel too strongly about it and can move this to `toggleMessagePinForThread` in `thread-updaters` if it makes more sense there.
Linear: https://linear.app/comm/issue/ENG-3403/update-pinnedcount-when-a-message-is-pinned-and-unpinned
Depends on D7211