Update config syntax for OpenSSH 7.5+

[ilolipopi]

Use "-" syntax to easily remove methods considered unsafe from algorithm lists, so newly added methods such as post-quantum key agreement won't be removed. This is only a syntax change and should not affect (in/de-crease) security nor change the page's status if out of date, as discussed in #198

[ilolipopi]

What's more, since OpenSSH 8.2 the Include keyword that allows including
additional configuration files via glob(3) patterns is added for sshd too. Making edits in new files under /etc/ssh/sshd_config.d instead of modifying /etc/ssh/sshd_conf can help prevent conflicting with package mantainer's version