Implement nested comments on backend

[ken1000minus7]

Create a comment entity with the following properties

• authorUsername
• title
• content
• timestamp
• blogId
• replyTo
  replyTo will be null, incase the comment is not a reply

We also need need endpoints for adding comments, getting comments etc

Lemme know if need more details

[ugpec79]

Sir pls assign this issue to me

[ken1000minus7]

As a part of this I'll assign you #22 as well

[ugpec79]

ok sir