PowerShell 7: Upgrade or allow selection of new version

Allow for a newer version of PowerShell to be used in Ketarin, either by upgrading the internal version that Ketarin references or allowing the end user to specify the path of the binary for PowerShell they want to use.

C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe

C:\Program Files\PowerShell\7\pwsh.exe