NetworkPkg/TlsAuthConfigDxe: Close and free the file related resource

NetworkPkg/TlsAuthConfigDxe: Close and free the file related resource

v2:
* Define one new internal function to clean the file content.

TlsAuthConfigDxe open file by FileExplorerLib. It need to close
file handler and free file related resource in some cases.
* User enrolls Cert by escape the Config page.
* The Cert is not X509 type.
* User chooses another file after he selected a file.

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