Feature request: Support for clock::date_count_between()

[edward-burn]

Now that the pr for some clock functions has been merged in https://github.com/tidyverse/dbplyr/pull/1496, there is another function I think is particularly useful for analytics: date_count_between @krlmlr would you happy for me to also work on a pr for this (likely similar to the one I've opened on dbplyr https://github.com/tidyverse/dbplyr/pull/1496)? This could use datediff for duckdb (https://duckdb.org/docs/sql/functions/date.html#datediffpart-startdate-enddate)?