Documentation for Import GET route

Context

When a repository is successfully imported, the registry should notify rails, as described in #374 (closed)

Proposal

This import returns the migration status of the repository, as described in #510 (closed), and would need rails to poll the registry to determine when a particular repository has finished importing.

Rough Outline

This is a rough outline of a potential design and should be considered a placeholder for scenarios to consider.

Route

GET /gitlab/v1/import/<path>

Success

• 200 — OK Successfully retrieved migration status

Errors

• 401 Unauthorized The client should take action based on the contents of the WWW-Authenticate header and try the endpoint again.
• 404 Not Found The repository was not found.