Alerting: modify alertmanager endpoints for proxying using the datasource UID (#47978)

* Alerting: enable proxying alertmanager calls using the datasource UID

* Remove use of datasource ID from the API

* Update frontend

pkg/services/datasourceproxy/datasourceproxy.go

@@ -60,10 +60,13 @@ func (p *DataSourceProxyService) ProxyDataSourceRequest(c *models.ReqContext) {
 	p.ProxyDatasourceRequestWithID(c, id)
 }
 
-func (p *DataSourceProxyService) ProxyDatasourceRequestWithUID(c *models.ReqContext) {
+func (p *DataSourceProxyService) ProxyDatasourceRequestWithUID(c *models.ReqContext, dsUID string) {
 	c.TimeRequest(metrics.MDataSourceProxyReqTimer)
 
-	dsUID := web.Params(c.Req)[":uid"]
+	if dsUID == "" { // if datasource UID is not provided, fetch it from the uid path parameter
+		dsUID = web.Params(c.Req)[":uid"]
+	}
+
 	if !util.IsValidShortUID(dsUID) {
 		c.JsonApiErr(http.StatusBadRequest, "UID is invalid", nil)
 		return