[Feature] Add explicit support for Vertica

[lukesonnet]

While Vertica largely works as a postgres connection, there seem to be differences primarily with respect to taking quantiles (relevant for percentile capping and quantile metrics).

We can either:

• make a new dedicated Vertica data source like we did for Redshift,
• OR, we add a configuration option to specify the "type" of postgres like we do with Presto/Trino.

Leaning towards the latter since I've only identified one discrepancy, but will take a closer look later.

[mattdp]

Please let me know when this is in place, since I have an interested customer.