Fix RLS regressions from XdsDepMan conversion

297ab05ef converted CDS to XdsDependencyManager. This caused three regressions:

• CdsLB2 as a RLS child would always fail with “Unable to find non-dynamic root cluster” because is_dynamic=true was missing in its service config
• XdsNameResolver only propagated resolution updates when the clusters changed, so a CdsUpdate change would be ignored. This caused a hang for RLS even with is_dynamic=true. For non-RLS the lack config update broke the circuit breaking psm interop test. This would have been more severe if ClusterResolverLb had been converted to XdsDependenceManager, as it would have ignored EDS updates
• RLS did not propagate resolution updates, so CdsLB2 even with is_dynamic=true the CdsUpdate for the new cluster would never arrive, causing a hang

b/428120265 b/427912384