ShellPkg/ShellPkg.ci.yaml: Add configuration for LicenseCheck

Add configuration IgnoreFiles for package config files.
So users can rely on this to skip license conflict for
some generated files.

Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>