Localize notification_utils to the Admin!

[ccostino]

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Description

This changeset copies everything in notifications_utils to turn into a local project module. It includes dependency changes to account for this adjustment and the notifications_utils tests. It also fixes all of the import statements.

TODO

• Fix the breaking tests
• Pull in Flask upgrade when it's ready
• Run through a few more tests to make sure the Admin is fully functional
• Create a follow-up issue to use vulture . --min-confidence=50 to identify things we can remove from the Admin

Security Considerations

• We're aiming to reduce development churn by incorporating this code directly and then removing all of the pieces we no longer need in this repo.

[ccostino]

Closing this in favor of #1542!