Allow deferral based on registry values

Some processes are always running but inactive. For instance, the Pulse Secure VPN client runs several executables that are live irrespective of an active VPN connection. If we were able to use registry keys, expressions, etc. to determine when to prompt a user to close their connection, it would allow us to more effectively update the applications. Tying this to the deferral mechanism, it could evaluate something other than a running process and notify the user that the application is in use or continue the installation with confidence that we are upgrading an inactive session.