Also, the legacy values on/true/yes/1 for password_encryption that
mapped to md5 are removed.  The only valid values are now
scram-sha-256 and md5.
Reviewed-by: Jonathan S. Katz <jkatz@postgresql.org>
Discussion: https://www.postgresql.org/message-id/flat/d5b0ad33-7d94-bdd1-caac-43a1c782cab2%402ndquadrant.com