Investigate prost-derive in generated source

[darach]

As an alternative to tonic-build, investigate changes to prost code generation to be based on
prost-derive structs. This would make compatibility with serde and translation between pb to
json more tractable in tremor ( the initial tremor sources/sinks for opentelemetry have an unwieldy
amount of json/protobuf translation code.

Via wise suggestion from @Hoverbear - recording here for posterity

[darach]

Note - we're also tracking the above via the GSOC project idea for gRPC for tremor