feat: Send a notification to reviewers on new comment

[flacial]

Overview

Currently, when a student receives a comment from a reviewer on their submission and attempts to reply to it, the reviewer doesn't get a notification. This behavior introduces difficulty in communication between the student and the reviewer, as the reviewer's only way to find out about the new comments by the student is to frequently visit the website. It can quickly degrade productivity for both the student who is trying to learn and the reviewers who are trying to teach.

Solution

Send a notification to all the people who wrote a comment on a certain submission's line except the comment author.

Missing requirements

comment section: comment(s) under a certain line in a submission

There are some things this PR does not introduce that are crucial for having an ideal notification system.

1. Participants in a comment section can't opt out of receiving notifications about it.
2. Participants cannot reply to or mention a user in a specific comment.

These shall be addressed in the project of adding a notification system (I could not find the issue for this project, but it did exist). @SlyBouhafs, any references?

Changes

• Export the logic for sending a notification to a function in the addComment resolver.
• Update the logic of sending a notification to send multiple ones by querying all the users who comment on a certain line or submission and sending a notification to them as long as they have a Discord ID.
• Update the message. Discord embedding has two versions. One is for the reviewers, and the other is for the student.

Unrelated changes

These changes are not related to this PR, but they were required in order for the CI/CD to pass

• Fix the flaky test in the exercises/[lessonSlug].tsx page by waiting for the router to be ready

Ideal solution

I believe this is not the ideal solution because sending simultaneous requests to our Discord bot server could overload the server and, by extension, slow down the server for other users. As of now, we don't have a lot of active users, and the comment section is almost always 1:1.

Related PR

• Add Reviewer Notification Functionality to Discord Bot #2849

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[codecov]

Codecov Report

Merging #2997 (c59d9fa) into master (df4ba19) will not change coverage.
The diff coverage is 100.00%.

❗ Current head c59d9fa differs from pull request most recent head 942fa49. Consider uploading reports for the commit 942fa49 to get more accurate results

@@            Coverage Diff            @@
##            master     #2997   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          191       191           
  Lines         3582      3606   +24     
  Branches       972       979    +7     
=========================================
+ Hits          3582      3606   +24     

Impacted Files	Coverage Δ
graphql/resolvers/addComment.ts	100.00% <100.00%> (ø)