Notification system for portal update events MVP

[robyngit]

Enable researchers to subscribe to email notifications for events pertaining to a portal's collection of data.

Events may include:

• Usage events: downloads, views, citations for any of the datasets in the collection
• New derived products created from any of the datasets in the collection
• When new datasets added to a portal via the query rules
• When the portal document is updated (e.g. markdown content changes, page added, etc.)

We will need to support notifications for individual events, or monthly or quarterly summaries.

There will need to be an option for users to turn notifications off if it’s no longer relevant or needed. This could be done via the portal itself, via an unsubscribe link in the email, or in a centralized section of their user page where all notification subscriptions are listed; or ideally, all three locations.

Note that there notifications should be available for both portal owners/editors and the community (when the portal/dataset is public). If the portal is subsequently made private, then there would need to be a mechanism to unsubscribe public "followers" and perhaps notify them again if the portal is made public in the future.