kacat -h is missing zstd codec as supported option.

[gunjan661]

Description
Even though kcat supports zstd codec the same is not listed as supported option in kcat .

How to reproduce
kcat -h

Current Producer options:
-z snappy|gzip|lz4 Message compression. Default: none

Possible resolution
we can update kcat.c to update the help based on whether librdkafka is supporting zstd or not. or provide a configuration option which would update the list of supported codecs.