6347 Cache the number of each component type assigned to devices/VMs (#12632)

---------

Co-authored-by: Jeremy Stretch <jstretch@netboxlabs.com>

netbox/virtualization/migrations/0035_virtualmachine_interface_count.py

@@ -0,0 +1,35 @@
+from django.db import migrations
+from django.db.models import Count
+
+import utilities.fields
+
+
+def populate_virtualmachine_counts(apps, schema_editor):
+    VirtualMachine = apps.get_model('virtualization', 'VirtualMachine')
+
+    vms = list(VirtualMachine.objects.annotate(_interface_count=Count('interfaces', distinct=True)))
+
+    for vm in vms:
+        vm.interface_count = vm._interface_count
+
+    VirtualMachine.objects.bulk_update(vms, ['interface_count'])
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('virtualization', '0034_standardize_description_comments'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='virtualmachine',
+            name='interface_count',
+            field=utilities.fields.CounterCacheField(
+                default=0, to_field='virtual_machine', to_model='virtualization.VMInterface'
+            ),
+        ),
+        migrations.RunPython(
+            code=populate_virtualmachine_counts,
+            reverse_code=migrations.RunPython.noop
+        ),
+    ]