[RFC] CLI Experimental Flag should resemble the interface of its daemon

[kvncrw]

[RFC] - Experimental Flag should be a boolean

related: #758

This is somewhat confusing, the experimental flag on the daemon is a bool. As I fumbled with this for about 15 minutes I did some research (see above related link) and learned it was decided it would be a string value because there are plans for this to become a "feature" toggle at some point. This coupled with the --experimental flag (on dockerd) seems inconsistent. I don't necessarily believe the design of a significantly related interface should pigeonhole another but it should certainly warrant consideration.

Please consider adding a experimentalOptions<string> in the future, YAGNI, and switching the experimental flag to a Boolean rather than a descriptor.

[bsousaa]

CLI experimental options are now enabled by default. #2774