CLI: Link Switch

When working with multiple checked out versions of the repo, the CLI will only work with whatever directory it was initially linked with, which can be a problem when looking to use the CLI with freshly checked out repo for testing or releases.

You currently have to run `jetpack cli unlink` and then `yarn install && yarn cli-link` before it will work again.

It would be cool if we could add a command, like `jetpack cli switch` that lets you switch working directories.

This may be irrelevant once we switch to pnpm.