Closes #18281: Support group assignment for virtual circuits (#18291)

* Rename circuit to member on CircuitGroupAssignment

* Support group assignment for virtual circuits

* Update release notes

* Introduce separate nav menu heading for circuit groups

* Add generic relations for group assignments

* Remove obsolete code

* Clean up bulk import & extend tests

netbox/circuits/migrations/0051_virtualcircuit_group_assignment.py

@@ -0,0 +1,85 @@
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+def set_member_type(apps, schema_editor):
+    """
+    Set member_type on any existing CircuitGroupAssignments to the content type for Circuit.
+    """
+    ContentType = apps.get_model('contenttypes', 'ContentType')
+    Circuit = apps.get_model('circuits', 'Circuit')
+    CircuitGroupAssignment = apps.get_model('circuits', 'CircuitGroupAssignment')
+
+    CircuitGroupAssignment.objects.update(
+        member_type=ContentType.objects.get_for_model(Circuit)
+    )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('circuits', '0050_virtual_circuits'),
+        ('contenttypes', '0002_remove_content_type_name'),
+        ('extras', '0122_charfield_null_choices'),
+    ]
+
+    operations = [
+        migrations.RemoveConstraint(
+            model_name='circuitgroupassignment',
+            name='circuits_circuitgroupassignment_unique_circuit_group',
+        ),
+        migrations.AlterModelOptions(
+            name='circuitgroupassignment',
+            options={'ordering': ('group', 'member_type', 'member_id', 'priority', 'pk')},
+        ),
+
+        # Change member_id to an integer field for the member GFK
+        migrations.RenameField(
+            model_name='circuitgroupassignment',
+            old_name='circuit',
+            new_name='member_id',
+        ),
+        migrations.AlterField(
+            model_name='circuitgroupassignment',
+            name='member_id',
+            field=models.PositiveBigIntegerField(),
+        ),
+
+        # Add content type pointer for the member GFK
+        migrations.AddField(
+            model_name='circuitgroupassignment',
+            name='member_type',
+            field=models.ForeignKey(
+                on_delete=django.db.models.deletion.PROTECT,
+                limit_choices_to=models.Q(('app_label', 'circuits'), ('model__in', ['circuit', 'virtualcircuit'])),
+                related_name='+',
+                to='contenttypes.contenttype',
+                blank=True,
+                null=True
+            ),
+            preserve_default=False,
+        ),
+
+        # Populate member_type for any existing assignments
+        migrations.RunPython(code=set_member_type, reverse_code=migrations.RunPython.noop),
+
+        # Disallow null values for member_type
+        migrations.AlterField(
+            model_name='circuitgroupassignment',
+            name='member_type',
+            field=models.ForeignKey(
+                limit_choices_to=models.Q(('app_label', 'circuits'), ('model__in', ['circuit', 'virtualcircuit'])),
+                on_delete=django.db.models.deletion.PROTECT,
+                related_name='+',
+                to='contenttypes.contenttype'
+            ),
+        ),
+
+        migrations.AddConstraint(
+            model_name='circuitgroupassignment',
+            constraint=models.UniqueConstraint(
+                fields=('member_type', 'member_id', 'group'),
+                name='circuits_circuitgroupassignment_unique_member_group'
+            ),
+        ),
+    ]