Switch to using `json-logging` rather than wrapping our error messages inside a log formatting block.

[zv]

At present, we're wrapping our error messages inside of a log formatting block, which, while that can provide some information about severity and the unit that initiated the logging message at present, is almost certainly going to grow to include severity information, more sophisticated logging units, etc.

@mjkoo proposed json-logger which doesn't have many users but appears to be an extremely simple project, much like we are doing now, but with the advantage that the "community" is maintaining the project.

[zv]

json-logger isn't maintained and it shows. I ended up implementing a new logger with a similar idea myself.