user-settings: Migrate users with away status to `!presence_enabled`.

Now that user status updates with `away=True|False` also update the
user's presence_enabled setting, we do a migration so that users with
`UserStatus.status=AWAY` also have the presence_enabled setting as
False (`away=!presence_enabled`).

Second step in making user status away a deprecated way to access
presence_enabled for clients supporting older servers.

Part of transitioning from 'unavailable' user status feature to
'invisible mode' user presence feature.

zerver/migrations/0413_set_presence_enabled_false_for_user_status_away.py

@@ -0,0 +1,37 @@
+# Generated by Django 4.0.7 on 2022-09-21 15:01
+
+from django.db import migrations
+from django.db.backends.postgresql.schema import BaseDatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+
+AWAY = 1
+
+# Set presence_enabled to False for all users with a UserStatus.status of AWAY.
+def set_presence_enabled_false_if_user_status_away(
+    apps: StateApps, schema_editor: BaseDatabaseSchemaEditor
+) -> None:
+    UserProfile = apps.get_model("zerver", "UserProfile")
+    UserProfile.objects.filter(userstatus__status=AWAY).update(presence_enabled=False)
+
+
+# Set UserStatus.status to AWAY for all users with presence_enabled False.
+def set_userstatus_away_if_presence_enabled_false(
+    apps: StateApps, schema_editor: BaseDatabaseSchemaEditor
+) -> None:
+    UserStatus = apps.get_model("zerver", "UserStatus")
+    UserStatus.objects.filter(user_profile__presence_enabled=False).update(status=AWAY)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("zerver", "0412_customprofilefield_display_in_profile_summary"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            set_presence_enabled_false_if_user_status_away,
+            reverse_code=set_userstatus_away_if_presence_enabled_false,
+            elidable=True,
+        ),
+    ]