Support action labels as input to execution:get-step-log and execution:get-quality-gate-result

[justinedelson]

As described in #226, it would be helpful if the label (i.e. "Build Image") could be provided as the action option to these commands.

This is likely dependent upon oclif/parser#162. It is doable without that change in @oclif/parser, but option validation would have to be reimplemented so it would be best if @oclif/parser supported that directly.