Support Redshift HLL functions/ approx_count_distinct

[pauldheinrichs]

Is your feature request related to a problem? Please describe. I don't see a reason why these can't be supported

• https://docs.aws.amazon.com/redshift/latest/dg/hyperloglog-functions.html
• https://docs.aws.amazon.com/redshift/latest/dg/r_COUNT.html

APPROXIMATE COUNT ( DISTINCT expression )

Describe the solution you'd like A clear and concise description of what you want to happen. I'd like to use APPROX_COUNT_DISTINCT without breaking 😄