External repository catalog and user access management

[underscope]

The goal of this feature flag is to enable custom catalog and external user management. The feature will:

• Block catalog and repository create access via UI
• Remove ability to manage ‘repository’ users from the UI
• Remove ability to clone repository from the UI
• Exposing repository listing, creation, update and deletion for the integration user via API
• Enabling user management to the integration user via API
• Enable tagging via the API for the integration user
• Enable import via the API for the integration user
• Enable cloning via the API for the integration user
• Enable tag based access rights management (if user and repository are tagged with the same tag, user can access course)
• Feature flag of the above
• Documenting the suggested integration process and providing API documentation.

To enable set EXTERNAL_ACCESS_MANAGEMENT=true env variable. For more details on how to setup integration user see tools/integration-user/README.md.