Added codechef's & codedrills' problem set (#5956)

* Added codechef's problem set

A vast range of unique problems, some of which are also part of Indian ICPC Preliminary Rounds and Regionals Rounds.

* Added codedrills' comeptitive problem set

Codedrills is the platform responsible for Indian ICPC contests currently (from 2020-present). It has many original & pure algorithmic problems.

more/problem-sets-competitive-programming.md

@@ -83,6 +83,8 @@
 * [Anarchy Golf](http://golf.shinh.org)
 * [CareerCup](http://www.careercup.com)
 * [CheckIO](http://www.checkio.org)
+* [Codechef](https://www.codechef.com/problems/school)
+* [Codedrills](https://codedrills.io/competitive)
 * [Codeforces](http://codeforces.com/problemset)
 * [Codility](https://codility.com/programmers/)
 * [Coding Bat](http://codingbat.com/java)