[SPIKE] Investigate sending multiple messages at the same time.

Investigate, define and describe sending bulk emails

I thought Darcy had screenshots related to this matter but I believe the following is expected: a library may want to schedule sending a patron notice(s) at a certain day and time. For example, a library may want to send Overdue notices every day at 12am midnight. The library may send this notice to a few patrons to 1000s of patrons.

This spike needs to address the following
1- how to support scheduling a patron notice(s) (assume will need to account for Calendar too)
2- satisfies the user stories linked to this spike (CIRC-370)
3- satisfies the scenarios outlined in this spike (see below)

Screenshots
https://drive.google.com/file/d/1U0rxUv_neSv8PjoR_ANy0Y4Ux6ty0AXE/view?usp=sharing
https://drive.google.com/file/d/1yD17w9-e9jdw1zl0GI3itCarHSQBbAie/view
https://drive.google.com/file/d/19gXNBGTeBXEzLgr58_-2NZUIpxCzTpUD/view

Scenario
Libraries frequently have tens of thousands, and at peak times hundreds of thousands of notices (upwards of 155K) to send during an idle time frame. That time frame might be between 1 am - 7 am, 12 am - 8 am. For example, a library may have a fixed due date of the last day of the semester, and they plan to send courtesy reminder notices 5 days before the due date, and again 3 days and 1 day before the due date.
Presumably with each notice sent, there's some attrition, because in theory, the first notice encourages some patrons to return their items, and the second notice encourages more patrons to return their item, etc.
It is not ideal to send these notices during the middle of the day when the ILS is assumed to be in heavy use. Administrators are accustomed to scheduling batch or bulk email notices in their current systems in order to maximize/utilize times when the system is not as being heavily used. Heavier use is typically seen during library open hours.
When scheduling, administrators need to consider system resources as well as other batch processes that are also scheduled. Most batch processes are pre-scheduled and routine, such as an email batch scheduled for every evening at 2 am or a user import process that happens once a semester.

Workflow

1. Process and prepare emails (figure out which notices need to be sent and to whom)
   1. Scan circulation rules and notice policies for which notices need to be sent.
   2. Pull the associated templates.
   3. Create an email from the template with to address pulled from the circ rules and notice policies.
2. Send emails.