Schema DDL: add support for AZ64 encoding

Hi,

Do we have to plan to implement AZ64 as default encoding for integer columns?
As per redshift documentation.
```
Compared to ZSTD encoding, AZ64 consumed 5–10% less storage, and was 70% faster.
```

https://aws.amazon.com/about-aws/whats-new/2019/10/amazon-redshift-introduces-az64-a-new-compression-encoding-for-optimized-storage-and-high-query-performance/