memsql connector supports keytab and principal for kerb authn

[agarwali]

Hi, I'm not sure if this is the right place to raise a feature request. I was wondering if we can add support for keytab and principal fields similar to spark jdbc reader which would load Krb5ConnectorContext with keytab and principal configuration. I can supply a custom jaas.conf in spark but would be nice if this can be supported as a spark option.