Datasources: Add toggle to control default behaviour of 'Manage alerts via Alerts UI' toggle (#98441)

* Datasources: Add toggle to control default behaviour of 'Manage alerts via Alerts UI' toggle

* Update documentation with suggestions

Co-authored-by: Larissa Wandzura <126723338+lwandz13@users.noreply.github.com>

docs/sources/datasources/prometheus/configure-prometheus-data-source.md

@@ -117,9 +117,15 @@ Following are additional configuration options.
 
 - **Manage alerts via Alerting UI** - Toggle to enable `Alertmanager` integration for this data source.
 
+{{% admonition type="note" %}}
+
+The **Manage alerts via Alerting UI** toggle is enabled by default. You can change this behavior by setting the [default_manage_alerts_ui_toggle]({{< relref "../../setup-grafana/configure-grafana/#default_manage_alerts_ui_toggle" >}}) option in the Grafana configuration file.
+
+{{% /admonition %}}
+
 ### Interval behavior
 
-- **Scrape interval** - Set this to the typical scrape and evaluation interval configured in Prometheus. The default is `15s`.
+- **Scrape interval** - Set to the typical scrape and evaluation interval configured in Prometheus. The default is `15s`.
 
 - **Query timeout** - The default is `60s`.
 

docs/sources/setup-grafana/configure-grafana/_index.md

@@ -782,6 +782,12 @@ On Linux, Grafana uses `/usr/share/grafana/public/dashboards/home.json` as the d
 
 <hr />
 
+## [datasources]
+
+### default_manage_alerts_ui_toggle
+
+Default behavior for the "Manage alerts via Alerting UI" toggle when configuring a data source. It only works if the data source's `jsonData.manageAlerts` prop does not contain a previously configured value.
+
 ## [sql_datasources]
 
 ### max_open_conns_default