More stunnel options and making some existing ones optional

Added in more stunnel options into template and tuns.pp:
verify (no longer hard coded can be specified)
retry
foreground
ssl_options (options)
socket_options (socket is not longer hard coded)
Also changed template to only add some values if they are set as they are not needed in all cases
We use a metadata.json file, not a Modulefile as the Modulefile is deprecated. Unless you're adding a new dependency or changing compatibility there's no need to update the metadata with a new feature request PR.