Provide command-line option for loading a custom powershell.config.json #5847

This enhancement is primarily driven by testing use cases including the following:

1: On Linux, syslog imposes a measurable overhead impacting test runtimes. (James Truher (@JamesWTruher): Please provide data)

2: For testing syslog and os_log there is a need to override the source name and output log to provide reliable verification.

One solution to both issues is to support launching an instance of PowerShell with a custom powershell.config.json file as a command-line option. For test runs, the json could restrict log output to error and critical messages. For syslog testing, the log file can be changed to ensure only the expected output is captured. For syslog and os_log, the source name can be changed to enable filtering and verifying the expected log messages.