[META] Leverage protobuf for serializing select node-to-node objects

[finnegancarroll]

Please describe the end goal of this project

Provide a framework and migrate some key node-to-node requests to serialize via protobuf rather than the current native stream writing (i.e. writeTo(StreamOutput out)). Starting with node-to-node transport messages maintains api compatibility while introducing protobuf implementations which have several benefits:

• Out of the box backwards compatibility/versioning
• Speculative performance enhancements in some areas
• Supports future gRPC work

Supporting References

• Search API POC - flame graph + OSB numbers
• Issue for API leveraging of gRPC + protobuf
• gRPC-based Search API

Issues

• [ ] Feature flag to enable protobuf transport protocol
• [ ] Support handlers for non-native transport protocols
• [ ] Initial protobuf implementation for types - FetchSearchResult, SearchHits, SearchHit

Related component

Search:Performance