Introduce protobuf serialization for objects - FetchSearchResult, SearchHits, SearchHit

[finnegancarroll]

Description

Extend existing native transport serialization by introducing protobuf definitions for the following classes: FetchSearchResult, SearchHits, SearchHit.

FetchSearchResultProtobuf, SearchHitsProtobuf, and SearchHitProtobuf wrap their respective classes overriding native serialization and writing/reading protobuf objects instead. Protobuf has the advantage of out of the box versioning/bwc, language agnostic service definitions, and speculative performance benefits in some areas. See this issue for additional details.

Having protobuf definitions for client facing objects could help enable gRPC work going forward as well.

• [ ] Hide behind experimental feature flag
• [x] Benchmark OSB big 5
• [x] Benchmark OSB vector workload

Related Issues

#15308 #13697

Check List

• [x] Functionality includes testing.
• [ ] API changes companion pull request created, if applicable.
• [ ] Public documentation issue/PR created, if applicable.

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