fix: update direct paging integration non-default route data (#5397)

## Which issue(s) this PR closes

This is a quick db migration follow-up to
#5382. It's mostly just an
enhancement. Basically #5382 had created a new/non-default route for
each Direct Paging integration. However, I overlooked actually setting
the chatops/escalation chain data for this new route:

![Screenshot 2025-01-06 at 3 55
19 PM](https://github.com/user-attachments/assets/6c9e68c3-64b7-47e2-9de6-34edd151b505)

This PR simply updates the recently created non-default direct paging
integration route, such that, to start, direct paging a team has no
escalation/notification difference whether the user doing the direct
paging sets important = True or False. From here, teams can modify these
routes to their needs (ex. setup and assign different escalation chains
for these different routes).

## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

engine/apps/alerts/migrations/0073_update_direct_paging_integration_non_default_routes.py

@@ -0,0 +1,56 @@
+# Generated by Django 4.2.17 on 2025-01-06 15:48
+
+import logging
+
+from django.db import migrations
+from django.db.models import Subquery, OuterRef
+
+logger = logging.getLogger(__name__)
+
+
+def update_direct_paging_integration_non_default_routes(apps, schema_editor):
+    """
+    If any of the original Direct Paging integration default routes had chatops settings or escalation chains
+    associated with them, simply set the non-default route to have the same settings. This will avoid any functional
+    differences should users start paging a team using the "important" functionality.
+    """
+    ChannelFilter = apps.get_model("alerts", "ChannelFilter")
+
+    logger.info("Starting update_direct_paging_integration_non_default_routes migration...")
+
+    # Subquery that selects the matching "default" channel filter for each non-default filter
+    default_route_subquery = ChannelFilter.objects.filter(
+        alert_receive_channel=OuterRef("alert_receive_channel"),
+        is_default=True
+    )
+
+    # Perform a bulk update on all non-default routes in one go
+    updated_count = (
+        ChannelFilter.objects
+        .filter(
+            alert_receive_channel__integration="direct_paging",
+            is_default=False
+        )
+        .update(
+            escalation_chain_id=Subquery(default_route_subquery.values("escalation_chain_id")[:1]),
+            telegram_channel_id=Subquery(default_route_subquery.values("telegram_channel_id")[:1]),
+            notify_in_telegram=Subquery(default_route_subquery.values("notify_in_telegram")[:1]),
+            slack_channel_id=Subquery(default_route_subquery.values("slack_channel_id")[:1]),
+            notify_in_slack=Subquery(default_route_subquery.values("notify_in_slack")[:1]),
+            notification_backends=Subquery(default_route_subquery.values("notification_backends")[:1]),
+        )
+    )
+
+    logger.info(f"Updated {updated_count} non-default direct paging integration routes")
+    logger.info("Finished update_direct_paging_integration_non_default_routes migration.")
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("alerts", "0072_upsert_direct_paging_integration_routes"),
+    ]
+
+    operations = [
+        migrations.RunPython(update_direct_paging_integration_non_default_routes, migrations.RunPython.noop),
+    ]