Add less to Debian variants

https://www.postgresql.org/docs/16/app-psql.html#APP-PSQL-META-COMMAND-PSET-PAGER
https://github.com/postgres/postgres/blob/REL_16_1/src/include/fe_utils/print.h#L25
(if "less" is available, it gets used as the default pager for psql, and it only adds ~1.5MiB to our image size)

Author: tianon