Draft: support autoinstall from user-data

changes in meta-data:

• [x] support local-hostname for compatibility with cloud-init
• [x] support for network-interfaces
• [x] support for resolv_conf (in case staic ip is set by network-interfaces)
• [x] ensure network is started if needed (do we support air-gapped installs?)
• [x] create default user (this could be done from post-install scripts)

Add support for applying user-data yaml.

The following keys are supported:

• bootcmd
• ntp
• apk
• packages
• runcmd
• timezone
• keyboard
• write_files
• groups
• users
• disk_setup
• fs_setup