pgsql: Add passwordcheck.min_password_length.

Add passwordcheck.min_password_length.

This new parameter can be used to change the minimum allowed
password length (in bytes).  Note that it has no effect if a user
supplies a pre-encrypted password.

Author: Emanuele Musella, Maurizio Boriani
Reviewed-by: Tomas Vondra, Bertrand Drouvot, Japin Li
Discussion: https://postgr.es/m/CA%2BugDNyYtHOtWCqVD3YkSVYDWD_1fO8Jm_ahsDGA5dXhbDPwrQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f7e1b3828a930639aefb5746a214cb5ddf734361

Modified Files
--------------
contrib/passwordcheck/expected/passwordcheck.out   |  4 +++
contrib/passwordcheck/expected/passwordcheck_1.out |  4 +++
contrib/passwordcheck/passwordcheck.c              | 24 +++++++++++---
contrib/passwordcheck/sql/passwordcheck.sql        |  4 +++
doc/src/sgml/passwordcheck.sgml                    | 37 ++++++++++++++++++++++
5 files changed, 69 insertions(+), 4 deletions(-)