Use authenticated npmrc

[chidozieononiwu]

This pull request updates the Azure DevOps pipeline for the SDK client archetype to ensure authenticated npm operations by configuring a custom .npmrc file. The changes focus on securely providing npm credentials for steps that require npm access, particularly when installing global npm packages and generating documentation artifacts.

Pipeline authentication improvements:

• Added the create-authenticated-npmrc.yml template step to generate an authenticated .npmrc file at $(Agent.TempDirectory)/gen_release/.npmrc for use during pipeline execution.
• Updated the npm install -g moxygen step to use the authenticated .npmrc by setting the npm_config_userconfig environment variable, ensuring npm commands have the necessary credentials.
• Set the npm_config_userconfig environment variable for the documentation artifact generation step, so any npm usage in this context also uses the authenticated .npmrc.

[Copilot]

Pull request overview

This PR updates the archetype-sdk-client Azure DevOps pipeline job to ensure npm operations run with an authenticated, job-scoped .npmrc, improving reliability when installing npm tools and generating docs artifacts.

Changes:

• Add the shared create-authenticated-npmrc.yml step to generate/authenticate an .npmrc under $(Agent.TempDirectory).
• Configure npm install -g moxygen to use the authenticated .npmrc via npm_config_userconfig.
• Configure the docs.ms artifact generation PowerShell task to use the same authenticated .npmrc (so any npm usage inside the script is authenticated).