cloud requires 'target' in stages, conflicting with docs

[countergram]

Documentation of 'options' contains the following stages:

stages: [
    { duration: "1m", target: 10 },
    { duration: "1m" },
    { duration: "1m", target: 0 }
  ],

However, k6 cloud throws this error:

ERRO[0001] 2 Invalid value for stages.1.target: None is not of type 'number'

[luizbafilho]

@robingustafsson this validation is coming from the cloud API. k6 itself allows empty target.

[na--]

Yep, that's why I tagged it as cloud 😄 Looking at this again, I'm not sure we should actually fix it and allow target to be omitted. It may save a few seconds for users, but it unnecessarily adds more confusion about how stages work. That would be especially bad once we add the arrival-rate based execution and/or some other execution mode like the log-based one. Or when we add different non-linear ramp-up/ramp-down strategies.

I feel like in this particular case, explicitness should trump conciseness and we should just edit the docs so we don't advertise support for this.

[luizbafilho]

Added the target to every place that used stages in the documentation.