POC: Add /remind_me quick action

What does this MR do and why?

This proof-of-concept adds a new quick action /remind_me <date in future> that will create a Notification/ToDo at the scheduled time. It uses scheduled Sidekiq jobs to create a ToDo for the user. It was built in this manner as an exercise in a fast experiment to gather feedback and interest before committing to a scheduled wider release.

Screenshots

Command hinting

Reminder set

ToDo

Related to #20490