RedfishPkg/DxeRestExLib: DxeRestExLib
    
    Add EFI REST EX helper library to create child instance of
    REST EX service.
    
    Signed-off-by: Abner Chang <abner.chang@hpe.com>
    
    Cc: Jiaxin Wu <jiaxin.wu@intel.com>
    Cc: Siyuan Fu <siyuan.fu@intel.com>
    Cc: Fan Wang <fan.wang@intel.com>
    Cc: Jiewen Yao <jiewen.yao@intel.com>
    Cc: Nickle Wang <nickle.wang@hpe.com>
    Cc: Peter O'Hanley <peter.ohanley@hpe.com>
    Reviewed-by: Nickle Wang <nickle.wang@hpe.com>