Add json output from CLI

[Ben Sayers]

This will allow third party tools to easily parse the output of the CLI.

It will also allow the end to end tests to more reliably parse the tools output. Right now these tests rely on regular expressions on strings to make their assertions.

[Ben Sayers]

We do not have any known consumers for this feature so closing this as won't fix. We are happy to reconsider if a concrete use case is brought to our attention, let us know if you have one!