Cloud Router supports named sets in Preview for BGP route policies

## Feature Feature Cloud Router supports named sets in [Preview](https://cloud.google.com/products#product-launch-stages)for BGP route policies. Named sets are used to group together expressions of either communities or BGP prefixes, allowing them to be managed or referenced as a single entity. For more information, see[BGP route policies overview](https://cloud.google.com/network-connectivity/docs/router/concepts/bgp-route-policies-overview#what-are-bgp-route-policies).