pfsense_openvpn_client support for auth_user and auth_pass fields

[stefangweichinger]

fixes #131

This is just a first step.

@opoplawski pls check and tell me if and how to improve that.

[opoplawski]

auth_pass is sensitive - you'll want 1no_log1 type options. See other modules (e.g. user) for details. It's probably a bcrypt hash as well (verify that) and should be validated like in the user module.

Thanks for starting on this.

[opoplawski]

You'll also want a changelog fragment and version_added doc fields.