BGP Extensions of SR Policy for Composite Candidate Path

SR Policy Architecture [RFC9256] defines the concept of a Composite Candidate Path. A regular SR Policy Candidate Path outputs traffic to a set of Segment Lists, while an SR Policy Composite Candidate Path outputs traffic recursively to a set of SR Policies on the same headend. This document defines extensions to BGP to distribute SR policies carrying composite candidate path information. So that composite candidate paths can be installed when the SR policy is applied.