String indexProperties(V version) {
    // 6.x _all disabled https://www.elastic.co/guide/en/elasticsearch/reference/6.7/breaking-changes-6.0.html#_the_literal__all_literal_meta_field_is_now_disabled_by_default
    // 7.x _default disallowed https://www.elastic.co/guide/en/elasticsearch/reference/current/breaking-changes-7.0.html#_the_literal__default__literal_mapping_is_no_longer_allowed
    String result = "    \"index.number_of_shards\": " + indexShards + ",\n"
      + "    \"index.number_of_replicas\": " + indexReplicas + ",\n"
      + "    \"index.requests.cache.enable\": true";
    return result + "\n";
  }
In Zipkin search, we do exact match only (keyword). Norms is about scoring. We don't use that
in our API, and disable it to reduce disk storage needed.
zipkin-storage/elasticsearch/src/main/java/zipkin2/elasticsearch/VersionSpecificTemplates.java