feat(init): infer invoked pkg mgr

[fahslaj]

Description

Infer the invoked package manager (pnpx, yarn dlx, npx) if no lockfile exists.

Motivation and Context

This allows users to create fresh Lerna workspaces with their package manager of choice.

How Has This Been Tested?

This has been tested manually.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (change that has absolutely no effect on users)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.