Allow setting ExternalTrafficPolicy for k8s dataplane proxy service

[sentinelleader]

Problem Statement

For cloud providers like azure and gcp, they dont support proxy protocol and the only way to setup client ip preservation is by setting ExternalTrafficPolicy to local in the lb service spec. Currently KGO don't expose setting this for the dataplane service
...

Proposed Solution

Extend ServiceOptions to include more k8s service overrides

Additional Information

https://techcommunity.microsoft.com/t5/fasttrack-for-azure/how-client-source-ip-preservation-works-for-loadbalancer/ba-p/3033722

[pmalek]

@sentinelleader #241 contains the draft of API change.

[pmalek]

#241 has been merged. It's already available in nightly and will land in 1.3