Add synced config to Icinga 2 module

[widhalmt]

This PR should add configuration that's sent to the local node. This should collect configuration on every kind of Icinga 2 node including configuration that is managed by Director or via API.

Please take into account, that I'm totally new to the code of this tool. Don't expect that I know what I'm doing.

[tbauriedel]

Thanks for the contribution!

I'm not sure if we should really collect all loaded configurations from the API.
The amount of data we collect would grow a lot in that case.
Collecting the current stage ID for example makes perfect sense. But I would refrain from collecting the complete API at the moment.

Can you give me the background of what you might need this for other than "what we have, we have"?

[widhalmt]

Hm... yes, you're right. In fact, the "currently active" configuration would be totally sufficient. But finding the currently active stage and just collecting this is beyond my Go knowledge for now.

[tbauriedel]

I would actually not collect the complete config of the active stage, but only collect to the ID of the stage.
I have to check whether there is further "metadata" within the API we could collect.
But the config itself below the active stage would definitely be too much in my opinion.

[widhalmt]

If we need to reproduce errors in testing or for further investigation a copy of the full configuration would be very useful. I guess, using compression for the tarball would massively shrink the space we require for transport

[tbauriedel]

I have added the active-stage form _api and director.
Also added list of the existing stage directories.

I would still not add the whole directory itself including content. This is way too much.
If you want to reproduce a system based on the support-collector data, you can already use /etc/icinga2/*. If the loaded stage is really needed, you should ask for it separately.