FORGE-1953: Add command to get and set JVM system properties

This PR is intended to implement the feature request https://issues.jboss.org/browse/FORGE-1953.

The idea is to add a new command to get/set system properties.
I still think these need to be `system-set-property` and `system-get-property`, or some alternative like:

`system-property --set name --value val`
`system-property --get name`

This could be even be done using a multi-step wizard to prevent erroneous usage, but I think it would be fine as a simple command with multiple args.

`system-property --get --set --value` etc...