[ADD] RPC `/nodes` endpoint, not return nodes that has request to leave , and zero bond

A while back , We decide to not set node to Disable status , because once a node get set to Disable status during churn, it has a few hours to return all it's yggdrasil funds before it get slashed. in some cases , if the node get into trouble , bifrost is not running , or node not in sync , then the network put the node in risk unnecessary. Detail !2009 (merged)

As a result of that , some nodes left , but the /nodes endpoint still keep it in the list , we should skip it

Also , if a node requested to leave , and they unbond itself , the node should be set to Disabled