cli: add prune command

[abiosoft]

This adds prune command to clear downloaded assets.

colima prune --help                                                                                                                            administrator@50029
Prune cached downloaded assets

Usage:
  colima prune [flags]

Flags:
  -a, --all     include Lima assets
  -f, --force   do not prompt for yes/no
  -h, --help    help for prune

Global Flags:
  -p, --profile string   profile name, for multiple instances (default "default")
  -v, --verbose          enable verbose log
      --very-verbose     enable more verbose log