Schema registry options

**Environment Information**
- OS [e.g. Mac, Arch, Windows 10]:
- Node Version [e.g. 8.2.1]:
- NPM Version [e.g. 5.4.2]:
- C++ Toolchain [e.g. Visual Studio, llvm, g++]:
- node-rdkafka version [e.g. 2.3.3]:

**Steps to Reproduce**
There is no way on the lib right now to use the defined schemas

**node-rdkafka Configuration Settings**
n/a

**Additional context**
Schema registries are a useful feature that wraps the data in a defined schema. They also can be retroactive applied, among other options.
We need a way to allow this lib to fetch the schemas and validate them with the user's ones.

Documentation
https://docs.confluent.io/platform/current/schema-registry/develop/using.html

No repository file, test, or entry point is named. Start by reading the linked Confluent Schema Registry documentation and the repository's existing producer and consumer APIs, then define the intended schema-fetching and validation interface before identifying tests that can establish completion.

Written by the indexing model from the issue text.