pgsql: Provide pg_amcheck with an --install-missing option

Provide pg_amcheck with an --install-missing option

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b859d94c638968ccbb517ac7e151bdd94ed7c16a

Modified Files
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doc/src/sgml/ref/pg_amcheck.sgml | 17 +++++++++++++++++
src/bin/pg_amcheck/pg_amcheck.c  | 39 +++++++++++++++++++++++++++++++++++++++
2 files changed, 56 insertions(+)