Added next and anonymize in requirements (#169)

* Added next_id support

* Some improvements
- Added support for anonymize flag in requirements
- Added data in flags with static type in challenge-example.yml to avoid
  verify command fails
- Added sort for requirements because it seems CTFd does not accept
  prerequisites if they are not sorted.
- Applied black to challenge.py to avoid Linting error.

* Updated to pass tests

* deleted debug print

* Applied black again

* Fixed ruff check errors

* Changed next_id to next

* Ommit require_anonymize and support anonymize in requirements

* Changed back to mistakenly edit lines

---------

Co-authored-by: Kevin Chung <kchung@ctfd.io>

Author: herosi

Makefile

@@ -1,5 +1,5 @@
 lint:
-	black --check .
+	black --diff .
 	isort --check .
 	ruff check .