Expose "enable firewall" option for kubernetes create command

[evandeaubl]

Is your feature request related to a problem? Please describe.
vultr-cli kubernetes create doesn't currently expose the option to enable firewall group creation, which results in manual effort in order to enable that after a cluster is provisioned.

Describe the solution you'd like
Exposing the enable firewall option as a command line switch on vultr-cli kubernetes create, in the same way as the --high-avail option for turning on an HA control plane.

[optik-aper]

@evandeaubl Thanks for the request. We'll get that added in the next release.