What github issue is this PR for, if any?

Resolves #2119

What changed, and why?

Followups now have a note attribute associated with them. Admins, supervisors and volunteers can write an optional note when creating a followup for a given case contact by interacting with a Swal alert.

How will this affect user permissions?

No permissions will be affected. All users that can create followups can add notes to them.

How is this tested? (please write tests!) 💖💪

Manual testing:

• Go a case page or the case contacts page
• Click on the "Followup" button of a given contact
• Check if the close and cancel button are working properly
• Check if adding a followup with and without a note work properly
• Go (as another user) to the notifications page
• Check if the notifications with and without notes display properly

Automated testing:

I've added the following specs:

• Request specs to see if the followups are being created properly and accepts the correct parameters
• System specs for the followups, to see if the Swal works properly (confirm, cancel and close button behave as expected)
• System specs for the notifications, to see if followups with and without notes are being displayed properly

Screenshots please :)

When an user clicks on the "Follow up" button the Swal displays the following prompt:

The notifications page now displays followups with and without notes:

Mobile view of notifications page: