🚀 Feature: update users `.npmrc` in place instead of replacing it

[johnnyreilly]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Right now, every time it is run, azdo-npm-auth replaces the existing users home .npmrc file with a brand new one. This is fine if the user only uses a single registry. But it is unfortunate if they use several and have multiple setups in the file.

Imagine if, instead, it updated the users home .npmrc file and left other bits in place. This would be better.

Additional Info

No response