support setting package root from cli

[amyXia1994]

Feature Request

Is your feature request related to a problem? Please describe:

If the generated kcl files will be placed in a monorepo like konfig, the import stmts in the generated files will be broken. And users need to manually replace all the import paths after generation.

Describe the feature you'd like:

support a --package-root option to allow users to specify the custom package root path to directly generate the right import stmts.

Describe alternatives you've considered:

None

Teachability, Documentation, Adoption, Migration Strategy:

None