Fix: PowerShell command action params / PowerShell sensor encoding fix

[amadeo-alex]

This PR:

• (PowerShell Command) fixes issue raised by @Nesnick Bug: Powershell Action Command Parameters not being passed HASS.Agent#328.
  • changes how arguments are passed on the process launching powershell.exe
• (PowerShell Sensor) fixes issue raised by @Skons & @Zarox666 Bug: PowershellSensor as Satellite Service - error_during_execution HASS.Agent#343
  • on systems where display culture does not match the keyboard culture (like "en-NL" or "en-PL") the CurrentCulture.TextInfo.OEMCodePage returns 1, this causes encoding parsing to fail
  • changes how encoding for PowerShell process is determined, HASS.Agent tries to derive the encoding from following cultures (in order): InstalledUICulture, CurrentCulture, CurrentUICulture, InvariantCulture
  • it should technically not happen but if the InvariantCulture fails, UTF-8 encoding is returned and warning log printed

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PowerShell Command changes have been tested against following script:

$wshell = New-Object -ComObject Wscript.Shell
$wshell.Popup("runs " + $PsBoundParameters.Values + $args,1,"Done",0x1)
$PsBoundParameters.Values >> sumlogs.txt

and following scenarios:

• normal path to the .ps1 script
• normal path to the .ps1 script and spaces present
• path to the .ps1 script containing non-safe characters and spaces

In all scenarios the payload value has been properly shown by the popup.
NOTE: due to how parameters are passed, they need to be retrieved with "$PsBoundParameters" instead of "args[]".

In addition this PR also adds an additional precheck in the "HandleActionReceived" function guarding against null payload (it can happen when payload is specified as an empty string ("") in Home Assistant.

[amadeo-alex]

Regarding the encoding issue reported in LAB02-Research/HASS.Agent#343, at some point a feature should be added which forces the PowerShell processes being spawned to use user-defined encoding.
This will allow users to then control the output encoding in PowerShell script using for example
[Console]::OutputEncoding = [System.Text.Encoding]::Unicode

That should allow for usage of any type of characters.