Add redirects for indexed alerting pages (#50918)

Co-authored-by: Brenda Muir <brenda.muir@grafana.com>
Signed-off-by: Jack Baldry <jack.baldry@grafana.com>

Co-authored-by: Brenda Muir <brenda.muir@grafana.com>

docs/sources/alerting/alerting-rules/_index.md

@@ -1,6 +1,7 @@
 ---
 aliases:
   - /docs/grafana/latest/alerting/alerting-rules/
+  - /docs/grafana/latest/alerting/old-alerting/create-alerts/
   - /docs/grafana/latest/alerting/rules/
   - /docs/grafana/latest/alerting/unified-alerting/alerting-rules/
 title: Create and manage rules

docs/sources/alerting/migrating-alerts/_index.md

@@ -1,6 +1,7 @@
 ---
 aliases:
   - /docs/grafana/latest/alerting/migrating-alerts/
+  - /docs/grafana/latest/alerting/unified-alerting/
 description: Upgrade Grafana alerts
 title: Upgrade to Grafana Alerting
 weight: 101

docs/sources/alerting/notifications/_index.md

@@ -1,6 +1,7 @@
 ---
 aliases:
   - /docs/grafana/latest/alerting/notifications/
+  - /docs/grafana/latest/alerting/old-alerting/notifications/
   - /docs/grafana/latest/alerting/unified-alerting/notifications/
 description: Notification policies
 keywords: