[Backport 8.1] Upgrade transport (#1619)

Co-authored-by: Tomas Della Vedova <delvedor@users.noreply.github.com>

package.json

@@ -80,7 +80,7 @@
     "xmlbuilder2": "^3.0.2"
   },
   "dependencies": {
-    "@elastic/transport": "^8.1.0-beta.1",
+    "@elastic/transport": "^8.0.1",
     "tslib": "^2.3.0"
   },
   "tap": {

src/client.ts

@@ -251,7 +251,12 @@ export default class Client extends API {
       context: options.context,
       productCheck: 'Elasticsearch',
       maxResponseSize: options.maxResponseSize,
-      maxCompressedResponseSize: options.maxCompressedResponseSize
+      maxCompressedResponseSize: options.maxCompressedResponseSize,
+      vendoredHeaders: {
+        jsonContentType: 'application/vnd.elasticsearch+json; compatible-with=8',
+        ndjsonContentType: 'application/vnd.elasticsearch+x-ndjson; compatible-with=8',
+        accept: 'application/vnd.elasticsearch+json; compatible-with=8,text/plain'
+      }
     })
 
     this.helpers = new Helpers({