www/py-dj32-django-treebeard: Add new port

django-treebeard is a library that implements efficient tree
implementations for the Django Web Framework 1.8 and later.

Features:

• Flexible: Includes 3 different tree implementations with the same API:
  • Adjacency List
  • Materialized Path
  • Nested Sets
• Fast: Optimized non-naive tree operations
• Easy: Uses Django Model Inheritance with abstract classes to define your own models.
• Clean: Testable and well tested code base. Code/branch test coverage is above 96%.

WWW: https://github.com/django-treebeard/django-treebeard

NB: This port is assigned to Django 3.2 and www/py-django-treebeard was

used as a template.

Reported by: sunpoet (via mail)