Merged PR 312372: Inject credentials into .npmrc using YML package_sources config instead of npm authenticate task

Previously I added npm authenticate task to the pipeline to inject credentials to the .npmrc.
This task is not compliant to CDPX. I'm switching to YAML instead as mentioned in this [doc](https://onebranch.visualstudio.com/OneBranch/_wiki/wikis/OneBranch.wiki/4787/Consuming-Packages-in-a-CDPx-Pipeline?anchor=npm)

.pipelines/pipeline.user.windows.yml

@@ -39,6 +39,9 @@ static_analysis_options:
 
 package_sources:
   npm:
+    config_files:
+        - include:
+          - ".npmrc"
     feeds:
       registry: https://powerbi.pkgs.visualstudio.com/_packaging/SDK.Externals/npm/registry/