pgsql: Mention md5 deprecation in postgresql.conf.sample

Mention md5 deprecation in postgresql.conf.sample

PostgreSQL 18 deprecated password_encryption='md5', but the
comments for this GUC in the sample configuration file did
not mention the deprecation. Update comments with a notice
to make as many users as possible aware of it. Also add a
comment to the related md5_password_warnings GUC while there.

Author: Michael Banck <mbanck(at)gmx(dot)net>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reviewed-by: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Reviewed-by: Robert Treat <rob(at)xzilla(dot)net>
Backpatch-through: 18

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/721bf9ce18b63c096104efd419af7e59053a333a

Modified Files
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src/backend/utils/misc/postgresql.conf.sample | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)