Customizing new package creation (lerna create)

[JamesHenry]

This issue serves to bring together all feedback related to wanting to be able to customize the outputs of lerna create.

Right now lerna create can only be customized via a list of explicitly supported CLI flags (you can see the current ones by running npx lerna create --help in your lerna workspace.

There is no way to resolve any kind of file generation or templating logic.

[JamesHenry]

#3478 was merged which improves the DX around location path arguments