CLI - add support for multi-valued headers

[baywet]

follow up of #2032 and #2045.
The CLI should make header options (documented) mutli-valued.
The CLI should also evaluate an additional option for non-documented headers

[darrelmiller]

For parameters that are described in the metadata we expect multi-valued parameters to be defined as an array of string and therefore multiple values can be passed to the strongly typed command line parameter we generate.

For a generic command like mgc makerequest, when we implement it, we will require the user to fold the multiple parameter values.