String formatIndexPattern(String format, GregorianCalendar current, String prefix) {
    return format.formatted(
      prefix,
      current.get(Calendar.YEAR),
      dateSeparator(),
      current.get(Calendar.MONTH) + 1,
      dateSeparator());
  }
Returns a set of index patterns that represent the range provided. Notably, this compresses
months or years using wildcards (in order to send smaller API calls).

<p>For example, if {@code beginMillis} is 2016-11-30 and {@code endMillis} is 2017-01-02, the
result will be 2016-11-30, 2016-12-*, 2017-01-01 and 2017-01-02.
zipkin-storage/elasticsearch/src/main/java/zipkin2/elasticsearch/internal/IndexNameFormatter.java