zabdig: check if zabbix events are up to date

[hbos]

Its not super important actually but if there is a lot of action and/or your working with a slow zabbix this can be an indicator your looking at old data. Maybe its enough show a warning.

We could show if there are many items queued
(Administration->Queue in zabbix web. There is an "Overview" and "Overview proxies" which might be relevant)

Or maybe just check some items from zabbix templates.

e.g there is a graph showing "zabbix internal process busy".
Maybe just breaking down those values in a list is good enough. If its very busy you can expect some queueing.