feat: add seen/delete notifications

[jeessh]

Notion ticket link

Ticket Name

Implementation description

• Added seen and delete functionality to notifications

Steps to test

1. npx prisma migrate dev
2. npx prisma generate
3. docker-compose up --build
4. test in postman

What should reviewers focus on?

• ./implementations/NotificationService.ts: deleteNotification, seenNotification
• delete only sets it to isDeleted, not deleting the actual notif

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR