Use protobuf encoding for core K8s APIs in apiserver-network-proxy

[tosi3k]

For core K8s API objects like Pods, Nodes, etc., we can use protobuf encoding which, compared to the default JSON encoding, reduces CPU consumption related to (de)serialization, reduces overall latency of the API calls, reduces memory footprint and the work performed by the GC and results in quicker propagation of objects to event handlers of shared informers.

Core system components of K8s default their serialization method to protobuf for 8 years already: kubernetes/kubernetes#25738.

Some benchmarks comparing JSON vs. protobuf showcasing how the latter data format (de)serializes faster and uses less memory:

• https://medium.com/@akresling/go-benchmark-json-v-protobuf-4ec3c62ec8d4
• https://www.codingexplorations.com/blog/performance-comparison-protobuf-marshaling-vs-json-marshaling-in-go
• https://medium.com/@david_turner/protocol-buffers-just-how-fast-are-they-9ec19ea580db

[k8s-ci-robot]

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[tosi3k]

/assign @cheftako