message_reminders: Add support for notes.

This commit adds the ability for users to include notes
with their message reminders.

Fixes #35070.

Co-Authored-By: Aman Agrawal <amanagr@zulip.com>

zerver/migrations/0749_scheduledmessage_reminder_note_text.py

@@ -0,0 +1,17 @@
+# Generated by Django 5.2.4 on 2025-07-31 03:31
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zerver", "0748_channelfolder_add_order"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="scheduledmessage",
+            name="reminder_note",
+            field=models.TextField(null=True),
+        ),
+    ]