* cmd/k8s-operator: users can configure operator to set firewall mode for proxies
Users can now pass PROXY_FIREWALL_MODE={nftables,auto,iptables} to operator to make it create ingress/egress proxies with that firewall mode
Also makes sure that if an invalid firewall mode gets configured, the operator will not start provisioning proxy resources, but will instead log an error and write an error event to the related Service.
Updates tailscale/tailscale#9310
Signed-off-by: Irbe Krumina <irbe@tailscale.com>