Email Notification Backend

[juliancleung]

Sends automated emails when there are status changes to requests, when users are approved, and events are coming up. These emails will include event information, and educator/volunteer details.

Certain events will trigger emails to educators, volunteers, or BEP admins.

Note that more email notifications may be added.

Specific events that trigger emails:

• sign-up confirmation (sent to volunteer or educator)
• sign-up request (sent to admin)
• sign-up approval (sent to volunteer or educator)
• volunteer receives invitation for event (sent to volunteer)
• educator accepts volunteer application (sent to volunteer)
• confirmation for event volunteering approval (sent to volunteer)
• volunteer applies for event (sent to volunteer)
• volunteer applies for event (sent to educator)
• update volunteers when event details change (sent to volunteer)

(Optional) Email Tokenization

• allow admins to accept or decline new user applications from email

For more context for each automated email, see the workflows:
https://www.figma.com/file/42giadAZ1aUTwEjGBZ7tkY/Explorations?node-id=288%3A3