[th/cloud-setup-preserve-external-ip] add preseve-external-ip flag to Reapply() and use from nm-cloud-setup

nm-cloud-setup uses Reapply(). That currently drops externally added IP addresses/routes. That seems undesirable, because they were added for a reason.

Add a flag to Reapply to preserve externally added addresses/routes.

https://bugzilla.redhat.com/show_bug.cgi?id=2132754

CI-test for reapply: NetworkManager-ci!1265 (merged)