Contact point testing (#37308)

This commit adds contact point testing to ngalerts via a new API
endpoint. This endpoint accepts JSON containing a list of
receiver configurations which are validated and then tested
with a notification for a test alert. The endpoint returns JSON
for each receiver with a status and error message. It accepts
a configurable timeout via the Request-Timeout header (in seconds)
up to a maximum of 30 seconds.

pkg/services/ngalert/api/generated_base_api_alertmanager.go

@@ -31,6 +31,7 @@ type AlertmanagerApiService interface {
 	RouteGetSilences(*models.ReqContext) response.Response
 	RoutePostAMAlerts(*models.ReqContext, apimodels.PostableAlerts) response.Response
 	RoutePostAlertingConfig(*models.ReqContext, apimodels.PostableUserConfig) response.Response
+	RoutePostTestReceivers(*models.ReqContext, apimodels.TestReceiversConfigParams) response.Response
 }
 
 func (api *API) RegisterAlertmanagerApiEndpoints(srv AlertmanagerApiService, m *metrics.Metrics) {
@@ -137,5 +138,15 @@ func (api *API) RegisterAlertmanagerApiEndpoints(srv AlertmanagerApiService, m *
 				m,
 			),
 		)
+		group.Post(
+			toMacaronPath("/api/alertmanager/{Recipient}/config/api/v1/receivers/test"),
+			binding.Bind(apimodels.TestReceiversConfigParams{}),
+			metrics.Instrument(
+				http.MethodPost,
+				"/api/alertmanager/{Recipient}/config/api/v1/receivers/test",
+				srv.RoutePostTestReceivers,
+				m,
+			),
+		)
 	}, middleware.ReqSignedIn)
 }