Log reason(s) for reroute if exceptional

[DaveCTurner]

Sometimes we call reroute() because something went wrong, and often that "something" is a problem common to multiple shards. For instance, a CircuitBreakingException during shard fetching will likely affect all the shard fetches on that node at once. We want to know about such exceptions in the logs, but there's little value in logging the exception for every single shard.

Today we discussed this as a team (in relationship to #57804 (comment)) and decided that it seems natural to use the batching facility built into the BatchedRerouteService to record examples of these failures in the logs, on a reroute-by-reroute basis, without having to record them all.

[elasticmachine]

Pinging @elastic/es-distributed (:Distributed/Allocation)