Store API access log

[darkweaver87]

Hello,

When using Icinga API it could be interesting to have access logs in a separate file.
Also, when it's used behing a reverse proxy or a load balancer it would be great to log http X-Forwarded-For or X-Real-IP headers :-)

Thanks :-)

[dnsmichi]

Icinga 2 only has its application log, filtered by severity levels. In order to support different categories to allow specific filtering like HttpRequests, this needs a general rewrite of the logging implementation.

Meanwhile you can use logstash grok filters to extract the details from the logs and use that for further analysis.

Blocked by #6636