PowerShell: Creating self-signed certificate for MSIX

The script below creates a self-signed certificate that can be used with testing and signing MSIX packages. Of course for testing purposes only. In a production environment you will need to use Device Guard signing or a certificate published by an interal PKI or external public trusted certificate authorities as described here: https://docs.microsoft.com/en-us/windows/msix/package/signing-package-overview