Add support for LeetCode

[cdbalaji]

We can even create new recommendation categories around interview preparation.

[ankur-kayal]

Research works done:

1. Leetcode has graphql apis which we can use to get all the problems along with respective tags (example implementation https://github.com/JacobLinCool/LeetCode-Query).
2. We cant get user statistics from leetcode (all submissions of the users) as we need to be logged in as the user to do that. (For now we can get only latest 20 submissions from the user). If someone can find a way to get all the submissions of the users from leetcode then we can start integrating leetcode to the recommender.

[amansaxena1]

getting all submissions of any user can be done only if user is logged in.
below script can help you out with it

https://github.com/amansaxena1/Leetcode_Question_Download