OpenSSH: add support for GSSAPI authentication

Hi,

It looks like GSSAPI authentication isn't built into the openSSH client on alpine:

$ docker run -it --rm alpine   
/ # apk add openssh-client 
...
OK: 10 MiB in 19 packages 
/ # ssh -o GSSAPIAuthentication=yes 
command-line line 0: Unsupported option "gssapiauthentication"

Would it be at all possible to build it in? This is helpful for authenticating SSH with Kerberos.

Thanks!