Add support to monitor kubernetes kube-proxy

[exekias]

Metricbeat Module / Dataset release checklist

Implement a new metricset under Kubernetes module to monitor kube-proxy. This is similar to what we did for apiserver: #7059

Modules

For a metricset to go GA, the following criterias should be met:

• Supported versions are documented
• System tests exist
• Automated checks that all fields are documented
• Documentation
• Fields follow ECS and naming conventions
• Dashboards exists (if applicable)
• Example data.json exists and an automated way to generate it exists (go test -data)
• Test environment in Docker exist for integration tests

[exekias]

@odacremolbap can you update this? I think only dashboards are missing

[odacremolbap]

I have filled the checks at the original issue comparing to the apiserver.
kube-proxy lacks dashboards and docker test environment

[odacremolbap]

closing, pending system tests for all kubernetes components will be managed at a different issue