Feat: add reminder snoozing & show new expiry / mention count when editing reminder

[TizzySaurus]

Closes #2045. Closes #2172.

Users can now "snooze" reminders, by pressing the "Snooze Reminder" button and then selecting a snooze duration from the dropdown menu that appears upon doing so.

I've tried to make this as resilient as I can, and have extensively tested it so there should hopefully not be any bugs 🤞.

Tested the "that's not your reminder to snooze" with help of @LiquidPulsar (thanks!).

This is my first attempt at using dpy2.0 features, so please feel free to give suggestions as to any possible improvements as well as reviewing the code as-is.

"Snooze Reminder" button:

After pressing the button:

After selecting snooze duration (both embeds in one message):