Docs: Link to the new alerting API spec (#35812) (#35888)

* Docs: Link to the new alerting API spec

* Update docs/sources/http_api/alerting.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* Update docs/sources/http_api/alerting.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>
(cherry picked from commit a42ace4d4c)

Co-authored-by: Sofia Papagiannaki <papagian@users.noreply.github.com>

docs/sources/http_api/alerting.md

@@ -7,8 +7,12 @@ aliases = ["/docs/grafana/latest/http_api/alerting/"]
 
 # Alerting API
 
-You can use the Alerting API to get information about alerts and their states but this API cannot be used to modify the alert.
-To create new alerts or modify them you need to update the dashboard json that contains the alerts.
+>**Note:** This topic is relevant for the [legacy dashboard alerts]({{< relref "../alerting/old-alerting/_index.md" >}}) only. 
+
+You can find Grafana 8 alerts API specification details [here](https://editor.swagger.io/?url=https://raw.githubusercontent.com/grafana/grafana/main/pkg/services/ngalert/api/tooling/post.json).  Also, refer to [Grafana 8 alerts documentation]({{< relref "../alerting/unified-alerting/_index.md" >}}) for details on how to create and manage new alerts.
+
+You can use the Alerting API to get information about legacy dashboard alerts and their states but this API cannot be used to modify the alert.
+To create new alerts or modify them you need to update the dashboard JSON that contains the alerts.
 
 ## Get alerts