Provide a system-wide kill switch for SCP protocol

[beldmit]

As we use SFTP by default, and SCP is considered insecure, we may want to disable it totally. As scp utility doesn't use the system-wide config, we suggest implementing it via the kill switch file.

[WSLUser]

I always considered it the other way around. Scp is also much more useful. It should not be abandoned. If it's indeed less secure, then make the necessary updates to keep the functionality the same while also improving the security.