NetworkPkg/HttpBootDxe: Add HTTP Boot Callback protocol support.

This patch updates the HTTP Boot driver to install a default HTTP Callback protocol
if the platform doesn't provide one. This callback implementation will print the
boot file download progress in percentage format.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Wu Jiaxin <jiaxin.wu@intel.com>