Send email alerts on privacy request failures

[sanders41]

Closes #1493

Code Changes

• Added table to store notification preference information
• Added table to track errors and if emails have been sent
• Added new email template for error notifications
• Trigger emails to be sent when the number of unsent errors reaches the specified threshold.

Steps to Confirm

• Set the notification service type to MAILGUN in the config
• Add mailgun config information
• Use the privacy-request/notification route to add an email address to receive notifications and set the notification threshold.
• Create enough errored privacy requests to reach the email threashold.

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation Updated:
  • documentation complete, or draft/outline provided (tag docs-team to complete/review on this branch)
  • documentation issue created (tag docs-team to complete issue separately)
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

Description Of Changes

Write some things here about the changes and any potential caveats

[eastandwestwind]

Great work on this so far @sanders41 !

Just have a couple requests / questions.

In addition, do we have another ticket to add docs for configuring these privacy request notifications?

[sanders41]

@eastandwestwind ready for another review.

In addition, do we have another ticket to add docs for configuring these privacy request notifications?

Good question. I haven't seen a ticket for this so I created one here #1997

[eastandwestwind]

thanks for making those changes, looks good to me!