Examples of Accepts-Serializer

https://github.com/fastify/fastify-accepts-serializer

Capabilities should be present for multiple content types.

The direction is to recommend Flatbuffers but Avro should be explained how to implement as well.

For understanding on the necessity of this [discussion is here](https://medium.com/@vaibhav0109/serialization-techniques-for-highly-scalable-systems-a8bf2130fe7f)

Review the linked fastify-accepts-serializer project and the agnostic repository structure first. Document examples showing capabilities for multiple content types, recommend Flatbuffers, and explain how Avro could be implemented. Done means the examples and both serialization approaches are clearly described.

Written by the indexing model from the issue text.