Elasticsearch: Fix failing requests when using SigV4 (#61923)

fix setting of `es` servicename

(cherry picked from commit c561045)

pkg/tsdb/elasticsearch/elasticsearch.go

@@ -73,16 +73,16 @@ func newInstanceSettings(httpClientProvider httpclient.Provider) datasource.Inst
 			return nil, fmt.Errorf("error getting http options: %w", err)
 		}
 
-		httpCli, err := httpClientProvider.New(httpCliOpts)
-		if err != nil {
-			return nil, err
-		}
-
 		// Set SigV4 service namespace
 		if httpCliOpts.SigV4 != nil {
 			httpCliOpts.SigV4.Service = "es"
 		}
 
+		httpCli, err := httpClientProvider.New(httpCliOpts)
+		if err != nil {
+			return nil, err
+		}
+
 		version, err := coerceVersion(jsonData["esVersion"])
 		if err != nil {
 			return nil, fmt.Errorf("elasticsearch version is required, err=%v", err)