Import and add profile support for the init command

[mr-cal]

What needs to get done

• Import the init command from its private location
• Add support for --profile
  • Profiles should be registered like craft-parts plugins

Why it needs to get done

To allow snapcraft to create a profile for testing with snapcraft init --profile test.

Design notes: https://docs.google.com/document/d/1lK0tb1eAapbuRoWipJsJ5HdQ27XZk9CJLWqdE52SjPU/edit#heading=h.qrrrlg3fcxw

[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-3542.

This message was autogenerated

[dariuszd21]

Relates to: #452

[mr-cal]

Oop, thanks. I missed that existing ticket.