[syslog-ng] Elasticsearch destination and time-zone info

[Fabien Wernli]

Hi,

In fact `time_zone()` is a meta-option which spans multiple block types
(implicitly).
We use the following:

destination d_es {
  java(
    time_zone("UTC")
    ...
  );
};

I'll submit a github PR to improve the documentation ASAP

Cheers