Extend esv2yaml to migrate the URL rewriter configuration

The URL rewriter plugin's configuration is to be migrated from /content/urlrewriter to /hippo:configuration/hippo:modules/urlrewriter/hippo:moduleconfig

esv2yaml should, when encountering the former node, move all properties starting with "urlrewriter:" to the latter node, which is bootstrapped by the hippo-cms group (i.e. known to be present in the ConfigurationModel at the time of merging in these definitions). The use of default settings will be detected and warned about during model merging, so users can remove redundant definitions.