add session expiration fields to auth method form and model

gatekeeper/migrations/0008_authmethod_session_expiration_minutes.py

@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('gatekeeper', '0007_remove_authmethod_totp_before_auth_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='authmethod',
+            name='session_expiration_minutes',
+            field=models.PositiveIntegerField(default=720, help_text='Session expiration time in minutes (only for Local Password and OIDC)'),
+        ),
+    ]