sources/ldap: add option to disable user sync, move connection init to model

passbook/sources/ldap/migrations/0002_ldapsource_sync_users.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.6 on 2020-05-23 19:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("passbook_sources_ldap", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="ldapsource",
+            name="sync_users",
+            field=models.BooleanField(default=True),
+        ),
+    ]