docs: md5_auth_cidr_addresses should be used for host-to-host access

What does this MR do?

While reviewing work we'd done with a customer on setting up Patroni, it was identified the majority of our docs recommend setting up scaled out GitLab with PostgreSQL access permitted using trust_auth_cidr_addresses rather than md5_auth_cidr_addresses which requires passwords. (internal ticket refs: 1, 2)

From https://docs.gitlab.com/omnibus/settings/database.html#configure-postgresql-block

md5_auth_cidr_addresses: A list of CIDR address blocks which are allowed to connect to the server, after authentication with a password. trust_auth_cidr_addresses: A list of CIDR address blocks which are allowed to connect to the server, without authentication of any kind. Be very careful with this setting. It’s suggested that this be limited to the loopback address of 127.0.0.1/24 or even 127.0.0.1/32.

Related issues

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