`required:False` does not apply when exposing outputs for a specification without namespace

[bastonero]

plumpy behaves in the following when exposing outputs for a specification process (example as in AiiDA WorkChains):

• Define a MainWorkChain
• Using a SubWorkChain/SubCalcJob: spec.expose_outputs(SubWorkChain, namespace_options={'required': False})
• MainChain.spec().outputs will still retain the required (True) outputs of SubWorkChain

The same doesn't happen when specifying a namespace in the expose_outputs.

Personal comments: I would expect as a plugin developer to actually override all required options of the exposed outputs, even when not defining a namespace. Otherwise, it seems pointless to specify the namespace_options if this does not happen (?).