Advertising p2mp policies in BGP

SR P2MP policies are set of policies that enable architecture for P2MP service delivery. A P2MP policy consists of candidate paths (CPs) that connects the Root of the Tree to a set of Leaves. The P2MP policy is composed of replication segments [RFC9524]. A replication segment is a forwarding instruction for a candidate path which is downloaded to the Root, transit nodes and the leaves. This document specifies a new BGP SAFI with a new NLRI in order to advertise P2MP policy from a controller to a set of nodes. This document introduces three new route types within this NLRI, one for P2MP policy and its candidate paths that need to be programmed on the Root node, one for the replication segment incoming SID which uniquely will identify the replication state and another for each outgoing interface that the packets get replicated to. The last two route types are forwarding instructions that needs to be programmed on the Root, and optionally on Transit and Leaf nodes. It should be noted that this document does not specify how the Root and the Leaves are discovered on the controller, it only describes how the P2MP Policy and Replication Segments are programmed from the controller to the nodes.