Use a BlockingCollection to avoid busy loop in REST API threads

[haxtibal]

The former implementation had 5 threads permanently spinning fast (10ms sleep) while waiting for a REST connection to process. This causes higher load in general and it breaks systems where Turn on PowerShell Script Block Logging policy is enabled, because then each PS statement including Start-Sleep is logged - resulting in 500 event log entries per second. It's a suggested setting in some hardening guidelines.

We can easily replace the Queue with a BlockingCollection backed by a ConcurrentQueue, which has the built-in feature to sleep until there are new items. Now the REST API threads consumes zero CPU time while waiting.

[LordHepipud]

Thank you for the PR! It looks great. Could you please update the PR with a changelog as bugfix for v1.9.0:

* [#497](https://github.com/Icinga/icinga-powershell-framework/pull/497) Fixes loop sleep for idle REST-Api threads by replacing them with [BlockingCollection](https://docs.microsoft.com/en-us/dotnet/api/system.collections.concurrent.blockingcollection-1?view=net-6.0) [ConcurrentQueue](https://docs.microsoft.com/en-us/dotnet/api/system.collections.concurrent.concurrentqueue-1?view=net-6.0)

I will then merge it immediately and publish it with v1.9.0

[LordHepipud]

One more addition. Could you please replace

$RESTThreadQueue = [System.Collections.Concurrent.BlockingCollection[PSObject]]::new(
            [System.Collections.Concurrent.ConcurrentQueue[PSObject]]::new()
        );

with

$RESTThreadQueue = New-Object System.Collections.Concurrent.BlockingCollection[PSObject] `
    -ArgumentList (New-Object System.Collections.Concurrent.ConcurrentQueue[PSObject]);

Otherwise the REST-Api will no longer work in Windows 2012 R2 or older.

[haxtibal]

Thanks, just applied your suggestions.

[LordHepipud]

Thanks!