Allow image cleanup before packaging

[ader1990]

In the offline gold image builder, add config to enable DISM Cleanup-Image to be run before packaging the image, so that updates installed during the extra_packages phase can be cleaned up before packaging.

The following new config options are added:

• updates:clean_updates_offline, default false. If set, dism cleanup-image will be performed offline, after any offline updates / components / capabilities were installed.
• updates:clean_updates_online, default true. If set, dism cleanup-image will be performed while the instance is running, after the updates were installed.

[ader1990]

@logan2211 please take a look at this PR and let me know if it works for you. This PR should replace https://github.com/cloudbase/windows-openstack-imaging-tools/pull/243