Remove breadcrumb plugin configuration from documents-only picker

The channel manager adds a cms-pickers configuration for selecting documents-only. Since the BreadcrumbPlugin has been removed from the pickers, the configuration should be updated as well. This means removing the configuration node of the BreadcrumbPlugin and move the root.paths property from this node to the cluster node of the picker, e.g. cms-picker/documents-only. To make the root.paths property available to the whole cluster a value 'root.paths' should be added to the frontend:properties property of this cluster node.