This will install amcheck in the database if not present. The default
schema is for the extension is pg_catalog, but this can be overridden by
providing a value for the option.
Mark Dilger, slightly editorialized by me.
(rather divergent)
Discussion: https://postgr.es/m/bdc0f7c2-09e3-ee57-8471-569dfb509234@dunslane.net
Comment fixes are applied on HEAD, and documentation improvements are
applied on back-branches where needed.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20210408164008.GJ6592@telsasoft.com
Backpatch-through: 9.6