create monkeypatching function for adding get_item dunder (#526)

* run black

* create monkeypatching function for adding get_item dunder

* whoops i forgot the test

* change the name in INSTALLED_APPS to make test pass

* turn the whole thing into a proper package

* move django_stubs_ext to requirements.txt

* also install requirements.txt

* attempt to fix pre-commit

* numerous small code review fixes

* fix dependency issues

* small dependency fixes

* configure proper license file location

* add the rest of the monkeypatching

* use strict mypy

* update contributing with a note monkeypatching generics

* copy release script from parent package

django_stubs_ext/tests/test_monkeypatching.py

@@ -0,0 +1,11 @@
+import django_stubs_ext
+from django_stubs_ext.monkeypatch import _need_generic
+
+django_stubs_ext.monkeypatch()
+
+
+def test_patched_generics() -> None:
+    """Test that the generics actually get patched."""
+    for el in _need_generic:
+        # This only throws an exception if the monkeypatch failed
+        assert el.cls[type] == el.cls  # `type` is arbitrary