add hardened SSH client configuration

add hardened SSH client configuration

Introduce a custom OpenSSH client configuration file for IPFire.
Some people use it as a jumping host, so applying hardening options
system-wide improves security.

Cryptography setup is the same as for OpenSSH server configuration.

The second version of this patch re-adds some non-AEAD cipher suites
which are needed for connecting to older RHEL systems.

Partially fixes #11751

Signed-off-by: Peter Müller <peter.mueller@link38.eu>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>