Route new/create project through Org scope

What does this MR do and why?

• Adds Organization scoped routes for new and create project
  • Only applies to Organizations that are not the Default Organization.
• Automatically maps global URL helpers to Organization URL helpers
• Defines a way forward for further Organization scoped routes - there are many to come

There is a more detailed description of Organization paths in the Organization Path Scope ADR.

The primary changes are:

• app/helpers/routing/organizations_helper.rb overrides the global route helpers that have an Organization equivalent.
• config/routes/organizations.rb is where we create the /o/ Organization scoped routes.

The URL helper overrides can not be placed behind a feature flag because it's part of the Ruby on Rails initialization process. However the select of global vs Organization scoped paths by the modified URL helpers are behind a feature flag.

Relates to #553914 (closed)

References

• Organization path scope - https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/organization/decisions/004_path_scope/
• Organization context resolution - https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/organization/decisions/001_organization_context_resolution/
• Current organization - https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/organization/current_organization/

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. In rails console enable the feature flag

Feature.enable :allow_organization_creation
Feature.enable :organization_switching
Feature.enable :ui_for_organizations
Feature.enable :organization_scoped_paths

2. Create an Organization through the + sidebar button.
3. Navigate to Organization Groups & Projects

4. Create a group through the New group button
5. From within that Group click the New project button and observe the URL is /o/ Organization scoped.
6. Create a project and observe the project is successfully created within the group.

MR acceptance checklist

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