Enforce target platform typing through nuxeoctl to Connect communications

Following NXBT-3382, we decided to review the way we pass target platform param from nuxeoctl to Connect, a strong typing will be easier to handle and will reduce confusion brought with the 2 string params targetPlatform and targetPlatformVersion.

Also there is a small bug in the TargetPlatformFilterHelper which is matching every packages when challenged against a blank (but not null) targetPlatform, it can be handled in this ticket