Support pushdown of substring and regexp_like to postgres

[alec-heif]

It would be extremely helpful for my team if the postgres connector supported pushdown for substring and/or regexp_like clauses. My org regularly has queries that apply a regex filter to a varchar column (or to a portion of a varchar column) and right now we are unable to run any of these queries through Trino due to the lack of pushdown for this highly-selective filter.

[martint]

The first steps is to be able to push down functions into connectors. This is being worked on here: #7994