text: Title: [APM] Set preference to any value for APM searches
  Body: If the APM indices have replica shards, the shard request cache hit ratio goes down, as each shard (primary/replica) has its own cache. If we set `preference` to any value, ES will ensure requests are routed to the same shard if possible, which should result in a better cache hit ratio. 
  
  See:
  https://www.elastic.co/guide/en/elasticsearch/reference/current/search-shard-routing.html