[Backport 8.16] Fix ECMAScript import (#2477)

test/esm/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "esm",
+  "version": "1.0.0",
+  "dependencies": {
+    "@elastic/elasticsearch": "file:../.."
+  }
+}

test/esm/test-import.mjs

@@ -0,0 +1,28 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { Client } from '@elastic/elasticsearch'
+
+new Client({
+  node: 'http://localhost:9200',
+  auth: {
+    username: 'elastic',
+    password: 'changeme',
+  }
+})