Add zstd compression to S3 Output

[metalshanked]

Currently, the Logstash S3 output only supports Gzip which is getting past its prime.

https://www.elastic.co/guide/en/logstash/current/plugins-outputs-s3.html#plugins-outputs-s3-encoding

Newer codecs like zstd are more efficient and enable cost savings and speed for S3 data.

[robbavey]

Hi @metalshanked - would you mind moving this issue to the AWS integration plugin? This repo is for issues associated with core Logstash. Thanks!