Reduce unnecessary churn when generating LocalPackages config

[merlynomsft]

Task name: N/A

Description:

• Avoid updating LocalPackage mapping in existing buildconfigs unless task is bumped to a new version
• Do not update _buildConfig package.json / package-lock.json / etc unless already present

Documentation changes required: (Y/N) N/A

Added unit tests: (Y/N) N/A (tested by bumping MavenV4 w/relevant scenerio + reverted)

Attached related issue: (Y/N) AB#2121133

Checklist:

• [ (N/A) ] Task version was bumped - please check instruction how to do it
• [x] Checked that applied changes work as expected