Stop duplicate comment notification emission

[timolegros]

Link to Issue

Closes: #4345

Description of Changes

• Added the parent comment author's addresses as excluded from the root thread notification.
• This does not remove duplicate notifications that have been emitted in the past but ensures that users don't see duplicate notifications in the future.
• This also does not stop notifications from having near-duplicate data as the issue describes. To normalize that data would require reworking how we fetch and emit comment notifications which is an excessive amount of work when there is a trivial solution. In other words, the denormalized data should be acceptable here given the trivial solution.

"How We Fixed It"

Parent comment authors are excluded from the notification sent to all users subscribed to a thread.

Test Plan

• Sign-in on account 1.
• Sign-in on account 2 on a separate browser.
• Create a thread from account 2 in any community.
• Subscribe to that thread from account 1.
• Create a comment on that thread with account 1.
• Reply to the new comment from account 2.
• Ensure there is only 1 notification in the notification drop-down of both accounts 1 and 2.

Deployment Plan

Other Considerations