REST API: in the Server header, identify the software, not the machine

[Al2Klimov]

Rationale: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server

Test

> GET /v1/checker?command=cpu HTTP/1.1
> Host: 10.27.0.147:5668
> User-Agent: curl/8.6.0
> Accept: */*
>
< HTTP/1.1 200 Ok
< Server: IcingaForWindows/1.12.3
< Content-Type: application/json
< Content-Length: 427
<

[LordHepipud]

Thank you very much for the PR. Could you please update the changelog alongside with the following:

### Bugfixes

* [#743](https://github.com/Icinga/icinga-powershell-framework/pull/743) Fixes REST-Api response header to report the software instead of the machine name

[LordHepipud]

Thanks!