openvpn-as: support setting the loadbalancer ip on the vpn service

[Laures]

for some cloud providers the external ip of "LoadBalancer" services can be provided. This can be important to maintain a static ip.

please allow setting the "loadBalancerIP" on the vpn service through the values.yaml if it is a LoadBalancer.

For googles GKE this is documented here:

https://cloud.google.com/kubernetes-engine/docs/tutorials/configuring-domain-name-static-ip?hl=de#use_a_service

In addition to that it would be usefull to unify the service definitions for udp and tcp. for LoadBalancer Setups the current system creates two different loadbalancers with different external ips