Add Discussion Page

**Is your feature request related to a problem? Please describe.**
GitHub offers a discussion menu for more Q and A-styled questions and inquires. And this clone should have it too.

**Describe the solution you'd like**
The page should be accessible to everyone who can see the repo. The default should look on the main page should look something like this:

The owner should be able to add/edit/delete (default) categories. People can create a new thread or comment under it. If the thread category's issue, then it should be something similar to Stack Overflow post. People should also be able to upvote/downvote comments/threads.

**Describe alternatives you've considered**
N/A

**Additional context**
N/A