A counter for sideop attendees

[Gehock]

This was previously attempted with just a naïve reaction but that couldn't be moved between messages when reordering events.

• Add a reaction to sideops which increments a counter when clicked
• Record people who have clicked (no need to display names)
• Decrease if clicked again

https://discord.com/channels/219564389462704130/360434525798531084/930814295766355969

[Gehock]

Done in 68df631d399d486e023ff7d778cddfef799476c0