remote_server: Send API feature level along with Zulip version.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zilencer/migrations/0048_remotezulipserver_last_api_feature_level.py

@@ -0,0 +1,17 @@
+# Generated by Django 4.2.8 on 2023-12-09 18:08
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zilencer", "0047_preregistrationremoteserverbillinguser_and_more"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="remotezulipserver",
+            name="last_api_feature_level",
+            field=models.PositiveIntegerField(null=True),
+        ),
+    ]