Add a way for frontend to know what URL to use when switching organizations

Update

Closed in favor of #437541 (closed) and #437095 (closed)

Background

In Allow switching of organizations (#423116 - closed) we are adding an organization switcher to the sidebar navigation. This switcher will list the available organizations by using the GraphQL query that was added in !136024 (merged). We need a way to know what URL to go to when switching organizations. For example if you are in the default organization on the main dashboard the URL would be https://gitlab.com. If you were to switch to the foo-bar organization the URL would be https://gitlab.com/-/organizations/foo-bar/dashboard/projects, but the frontend doesn't currently have a way to calculate this URL.

Proposal

Current organization

• Backend will calculate the current organization and expose it via the current_organization method in lib/organization/current_organization.rb#L11
• We will expose the current organization to the frontend in lib/gitlab/gon_helper.rb similar to how we expose current_user
• The frontend will use gon.current_organization to display the current organization in the organization selector.

Switching organizations

• Create a Rails helper (let's call it current_route_scoped_to_organization for now) that calculates the current route in the context of an organization.
  • If it is a route that can be scoped to organizations such as your work or your profile it returns a route with a placeholder for the organization path. e.g. https://gitlab.com/-/organizations/:organization_path/dashboard/projects
  • If it is a route that cannot be scoped to an organization (such as https://gitlab.com/gitlab-org/gitlab or https://gitlab.com/gitlab-org/ return nil
• Pass the return value of current_route_scoped_to_organization to the frontend via a data attribute.
• In the frontend, if current_route_scoped_to_organization is null link to the organization front page. If current_route_scoped_to_organization is a string replace :organization_path with the organization path and link to that URL.

Implementation guide

Need to confirm proposal makes sense then refine.