Fixes #18245: Make DeviceRole Hierarchical (#19008)

Made DeviceRoles hierarchical, had to also change the filtersets for Device, ConfigContext and VirtualMachine to use the TreeNodeMultipleChoiceFilter.

Note: The model was changed to use NestedGroupModel, a side-effect of this is it also adds comments field, but I thought that was better then doing a one-off just for DeviceRole and having to define the fields, validators, etc.. - keeps everything DRY / consistent.

* 18981 Make Device Roles Hierarchical

* 18981 forms, serializer

* 18981 fix tests

* 18981 fix tests

* 18981 fix tests

* 18981 fix tests

* 18981 fix tests

* 18981 fix migration merge

* 18981 fix tests

* 18981 fix filtersets

* 18981 fix tests

* 18981 comments

* 18981 review changes

netbox/dcim/tests/test_models.py

@@ -346,7 +346,8 @@ class DeviceTestCase(TestCase):
             DeviceRole(name='Test Role 1', slug='test-role-1'),
             DeviceRole(name='Test Role 2', slug='test-role-2'),
         )
-        DeviceRole.objects.bulk_create(roles)
+        for role in roles:
+            role.save()
 
         # Create a CustomField with a default value & assign it to all component models
         cf1 = CustomField.objects.create(name='cf1', default='foo')