Follow ups and to dos for A74 - xds config tears

[eshitachandwani]

• Change handling of endpoint ambient errors to log error from dependency manager rather than sending it in resolution note.
• Discuss if sending duplicate XDSConfig updates when CDS update for dynamic cluster is received is okay ? If not , we will probably need to save the last XDSConfig update sent and verify the new update against that to check if it is different and only then send the update.
• Discuss what the behaviour should be when we receive LDS/RDS resource error :
  - [ ] Should we immediately send erroring CS
  - [ ] Should we continue sending XDSConfig if there are RPCs ongoing.
• Discuss whether aggregate cluster is the more common case and based on that decide if we want to have a separate map cluster state of include it in the clusterRef struct.