naming convention for elastic search indexes, independent from logstash or any elastic beats.

[lpasquali]

We should decide how to name elastic search indexes for GeoServer in a way which is independent from logstash or any elastic beats.
we should avoid using patterns like:

filebeat-*
logstash-*

something like:

geoserver-%{[metadata][client_name]}-%{[@metadata][beat]}-%{[@metadata][version]}-%{+YYYY.MM.dd}

Then we should update index-pattern in default.ndjson.