Evaluate use of `PerSource*` options for sshd

A series of `PerSource` directives was introduced in OpenSSH 9.8 for blocking repeated connection attempts. We should evaluate these options and set them up on our machines to attempt to mitigate denial-of-service attempts on our machines where a suitable version is available.

Ref: https://www.openssh.com/txt/release-9.8 and the details in https://man.openbsd.org/sshd_config (That openbsd page is linked from the official openssh site)

Start with the OpenSSH 9.8 release notes and the sshd_config manual linked in the issue, then identify which machines have a suitable version. Done means the applicable PerSource options have been evaluated and configured on eligible machines, with any unsupported machines accounted for.

Written by the indexing model from the issue text.