Add bundle-schema option to bundler CLI

[garryod]

Adds a bundle-schema option to the bundler CLI, previous default behaviour is now available via serve. The --path option can be passed to specify a directory to write schema files to

[DiamondJoseph]

Makes sense to me, but can't speak for the implementation.

Adds another option to the CLI, which can print the json schema or output it to a file, when using the new serve option does the old behaviour.