CBF support for colored SR-TE

You can create a multipath route between different transport tunnels in any inet6.3 RIBs to resolve service routes. We also support storage of transport-class in nexthop gateways, support preserve nh hierarchy for policy multipath, and extend cos policy to support transport-class color so that selective traffic can be steered over one of SR-TE or IGP flex-algo transport tunnels. To match transport-class key in FRR indirect keys structure, use transport-class color <color> at the [edit class-of-service forwarding-policy next-hop-map next-hop-map-name forwarding-class forwarding-classname] hierarchy level. To store a color value as FRR indirect keys structure for the leaked inet6.3 routes, use set best-effort color color at the [edit routing-options transport-class] hierarchy level. To enable expanded nh hierarchy support for policy-multipath routes for RIBs, use set preservenexthop-hierarchy at the [edit routing-options rib rib-name policy-multipath] hierarchy level. For any inet[6].3 RIBs, the preserve-nexthop-hierarchy is enabled by default.