Define custom date stamp in ElasticsearchWriter module

[manny4566]

Hi,

thank you for fixing the problem with Elastic v8 and the ElasticsearchWriter module on this way.

Now i have a feature request for the file https://github.com/Icinga/icinga2/blob/master/lib/perfdata/elasticsearchwriter.cpp -> line 466

Could you please add a option in /etc/icinga2/features-available/elasticsearch.conf to make it possible to define a custom date stamp ?

For example "$index_%Y%m%d"

Btw. Your documentation no longer matches this file. :) https://icinga.com/docs/icinga-2/latest/doc/09-object-types/#objecttype-elasticsearchwriter

Documentation: $index-$d.$M.$y

File: "-%Y.%m.%d"

Thank you