Implement better command output formatting in the hooks

The following discussion from !18 (merged) should be addressed:

• @whot started a discussion: (+1 comment)

  there's a bit of optimism here that stdout and stderr are valid json strings 😄

We should probably use serde_json to dump the output, and also handle the debug parameter. Which also means that stdout is not great, and using a proper logging facility would be better.