Nitro should copy SSH keys into the machines

[brandonkelly]

Similar to how Homestead lets you specify the path to your SSH key via the authorize setting, and copies it into the VM. (See “Set Your SSH Key” section on https://laravel.com/docs/4.2/homestead.)

[lukeholder]

Also would be good if the key is added to authorised keys in the machine: canonical/multipass#1413 (comment)

[jasonmccallister]

I think during the init process we should prompt the user to add their SSH keys into the machine along with the option to run a command that will import the keys.

To @lukeholder's point, it should also add to the authorized keys, but my big thing is to keep this out of the config file. I'm thinking something along the lines of:

$ nitro init
# all the prompts
Should we add your SSH keys to the machine? [yes]

$ nitro keys
Should we add your SSH keys to the machine? [yes] yes
Ok, we have added your SSH keys into `nitro-dev`

[jasonmccallister]

We should list the keys to select similar to this: https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/eb3-init.html

[jasonmccallister]

Added the keys command to make this easy, should probably also prompt during init?