Add support for `zstd` compression

It’d be really nice to add support for zstd compression now that this is an officially supported codec (KIP-110).

[jeffwidman]

Would be really nice to refactor the codec compression interfaces into something more generic, allowing users to wrap their favorite library – rather than us having to pick a favorite to integrate with directly.

Agreed. However, there is still protocol-level considerations since the producer has to signal to the broker what compression format was used (which it, in turn, passes to downstream consumers).

What would be a good interface?

I’m thinking the consumer/producer can pass in a custom class. And that class has four pieces:

1. compress()
2. decompress()
3. Class-level var indicating which protocol flag to set… allowed values are None/gzip/snappy/other broker-supported values
4. Any custom configs that would be passed to the underlying library… such as the level of compression, multi-core vs single (this may not be relevant for our use case), etc. This seems to me to be the trickiest piece, how to do this somewhat generically/thin so it provides flexibility rather than straight-jacketing the user.

[einvince]

Can close, merged in https://github.com/dpkp/kafka-python/pull/2021