Move explanation of TrinoStatus to its own section in routing-rules page

Author: andythsu

docs/routing-rules.md

@@ -134,6 +134,21 @@ condition: 'request.getHeader("X-Trino-Client-Tags") contains "label=foo"'
 
 If no rules match, then request is routed to adhoc.
 
+### TrinoState
+
+This class attempts to track the current state of Trino cluster. It is updated per every healthcheck.
+There are three possible states
+
+* PENDING
+  * A Trino cluster will show this state when it is still starting up. It will be treated as 
+    unhealthy by RoutingManager, and therefore requests will not be routed to PENDING clusters
+* HEALTHY
+  * A Trino cluster will show this state when healthchecks report clusters as healthy and ready.
+    RoutingManager will only route requests to healthy clusters
+* UNHEALTHY
+  * A Trino cluster will show this state when healthchecks report clusters as unhealthy. RoutingManager
+    will not route requests to unhealthy clusters.
+
 ### TrinoRequestUser
 
 This class attempts to extract the user from a request. In order, it attempts

gateway-ha/src/main/java/io/trino/gateway/ha/clustermonitor/TrinoStatus.java

@@ -13,12 +13,6 @@
  */
 package io.trino.gateway.ha.clustermonitor;
 
-/**
- * PENDING is for ui/observability purpose and functionally it's unhealthy
- * We should use PENDING when Trino clusters are still spinning up
- * HEALTHY is when health checks report clusters as up
- * UNHEALTHY is when health checks report clusters as down
- */
 public enum TrinoStatus
 {
     PENDING,