Data schema support

[RobertIndie]

Motivation

Our wasm function requires knowledge of the data schema to parse JSON data.

Goals

• Support transfer of the data schema from function-stream host to wasm function

Implementation

We can employ pulsar-client-go to extract the schema in JSON format from the message.

One possible approach is to mount a specific file, say /schema, to the wasm function's wasi. We can then utilize the buffer_reader to write to this file.

When the wasm function wants to access the schema, we could transfer the schema through this file interface.

[RobertIndie]

Done by #182