Shard started reroute high priority (elastic#137306)

* Shard started reroute high priority

We executed shard started at urgent priority, but the subsequent reroute
were at normal priority, causing subsequent recoveries to possibly come after
other less important actions. Now do the reroute at high priority.

Author: henningandersen

docs/changelog/137306.yaml

@@ -0,0 +1,5 @@
+pr: 137306
+summary: Shard started reroute high priority
+area: Allocation
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/cluster/action/shard/ShardStateAction.java

@@ -829,7 +829,7 @@ private static boolean assertStartedIndicesHaveCompleteTimestampRanges(ClusterSt
         public void clusterStatePublished(ClusterState newClusterState) {
             rerouteService.reroute(
                 "reroute after starting shards",
-                Priority.NORMAL,
+                Priority.HIGH,
                 ActionListener.wrap(
                     r -> logger.trace("reroute after starting shards succeeded"),
                     e -> logger.debug("reroute after starting shards failed", e)