migrations: Add migration to set default value of enable_read_receipts.

This migration set default value of enable_read_receipts to True
for existing realms which require an invitation to join.

zerver/migrations/0405_set_default_for_enable_read_receipts.py

@@ -0,0 +1,28 @@
+# Generated by Django 4.0.6 on 2022-08-08 16:52
+
+from django.db import migrations
+from django.db.backends.postgresql.schema import BaseDatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+from django.db.models import Q
+
+
+def set_default_for_enable_read_receipts(
+    apps: StateApps, schema_editor: BaseDatabaseSchemaEditor
+) -> None:
+    Realm = apps.get_model("zerver", "Realm")
+    # We enable read receipts by default in realms which require an invitation to
+    # join or which allow only users having emails with specific domains to join.
+    Realm.objects.filter(Q(invite_required=True) | Q(emails_restricted_to_domains=True)).update(
+        enable_read_receipts=True
+    )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("zerver", "0404_realm_enable_read_receipts"),
+    ]
+
+    operations = [
+        migrations.RunPython(set_default_for_enable_read_receipts, elidable=True),
+    ]