Added RequiredRSASize option for ssh client.

[inntran]

This is actually a bug, because the "RequiredRSASize" exists in recent OpenSSH source.

The reason I make this change are as follows:

1. The RequiredRSASize option was added in openssh/openssh-portable@54b333d .
2. RHEL 9.1 changed minimum RSA key size to 2048 by default, broke connections to old SSH servers. Reference: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/9.1_release_notes/new-features#BZ-2066882
3. Fedora Linux sync'd the change from RHEL 9.1. Reference: https://packages.fedoraproject.org/pkgs/openssh/openssh-server/fedora-37.html
4. I was connecting to a legacy device over SSH and tried very hard to remember this option.

I have ran the supplied test for ssh, got the following output:

====== 12 passed, 1 xfailed in 35.62s ======

[inntran]

To get the latest available OpenSSH client options:

curl --silent https://raw.githubusercontent.com/openssh/openssh-portable/master/ssh_config.5 | awk '$1==".It" && $2=="Cm" && $3!="Host" && $3 ~ /^[A-Z]/ {print $3}' | xargs | fold -s -w 72

I didn't include this because this might break user's expectations on old versions of OpenSSH client.
Or we could include this instruction to help downstream distributions to patch their own.

[scop]

Thanks! Merging with commit message tweaked to our standards.