Enable zlib by default

Snappy compression is enabled by default for intra-cluster compression since 3.5.7.

This also means that drivers can take advantage of snappy compression by default.
However, most drivers only support zlib compression, which is not available by the server by default.

The server should allow both snappy and zlib compression by default, while negotiating the intra cluster compression as snappy, but still allow drivers to use zlib.