Nt32Pkg.dsc: Add flag to control HTTP connections
    
    v3:
    * Correct the commits grammar
    
    v2:
    * Rename the flag.
    
    This flag is to overwrite the value of PcdAllowHttpConnections,
    then the platform can make a decision whether to allow HTTP
    connections or not.
    
    Cc: Ye Ting <ting.ye@intel.com>
    Cc: Fu Siyuan <siyuan.fu@intel.com>
    Cc: Ruiyu Ni <ruiyu.ni@intel.com>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Cc: Kinney Michael D <michael.d.kinney@intel.com>
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
    Reviewed-by: Ye Ting <ting.ye@intel.com>
    Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
    Reviewed-by: Gary Lin <glin@suse.com>