[Feature request] allow to prefix output

[CircleCode]

state of the art docker runs only one servce, but in true life, you sometimes need to run supercrinic alongside other services. In this case, it is difficult to diffrentiate output from supercronic from other output. can you either add an option to define an output prefix, or prefix it by default?

[krallin]

This is certainly possible, and should be fairly to implement by adding a flag to use a logging formatter that injects a prefix (might be worth having a format option that can accept a value, and deprecate — but not remove — the current json flag).

That said, I don't really have the bandwidth to work on this right now, but I'd be happy to look at a PR for it.