Missing Flag Argument Option for ForceKubernetesService

[CH-DianaArrieta]

Describe the bug
We're running Skipper in Kubernetes. We're trying to enable KubernetesForceService to use service addresses, but the flag isn't available for use.

To Reproduce
Add context, for example:

1. Add kubernetes-force-service in Skipper arguments:
   args: ...
   - "-kubernetes-force-service=true"
   ...
2. Start the Skipper daemonset

Observed behavior
Pods will crashloop due to the flag missing.

We also tried the variation force-kubernetes-service without success.

[AlexanderYastrebov]

A feature to use service IP instead of Endpoints was implemented within #2089 via #2088 but was not exposed for configuration via flag.

[AlexanderYastrebov]

Was implemented by #3515