Worker: don't send empty log lines

[josephjclark]

Don't send empty log lines to Lightning. Do send console.log(undefined), especially in job code, because it might be important.

From discussion at: OpenFn/lightning#2959

• In the job logger - the thing that logs user's console.log statements - I could (probably) detect an undefined value and pass an 'undefined' string instead. Now Lightning will receive message: ['undefined']. I don't know if that will confuse anything. I suppose I could also do message: [undefined] if an argument was passed, which is probably more useful

• The logger has console.break() function, which I think is mostly what the CLI uses for this. I could have a rule like: when logging json output, ignore any console.break statements - because we assume that the JSON will be consumed by something richer that a terminal downstream.
  The worker could refuse to send any logs with message: [] on the assumption that it's a waste of everyone's time
  If I do that, then I think I can promise:

• message: [undefined] is useful and even important to log
  *You will not be sent meaningless empty lines which are just stdout padding

[josephjclark]

I promised this to Stu last month and haven't done it. Hoping to pick this up this week.