Modify admin layout to only manage tenants and admins

We only want to render the account link and login items in the header.
And we want only render the Multitenancy and Administrators sections in
the admin sidebar.

We include the administrators management so it's possible to give
permissions to other users to manage tenants.

In order to restrict access to other sections by typing the URL or
following a link, we're only enabling the rest of the routes when we
aren't in the multitenancy management mode.

spec/controllers/users/sessions_controller_spec.rb

@@ -69,4 +69,22 @@ describe Users::SessionsController do
       end
     end
   end
+
+  describe "after_sign_in_path_for" do
+    it "redirects to account path when multitenancy_management_mode is enabled and user is not an admin" do
+      allow(Rails.application.config).to receive(:multitenancy_management_mode).and_return(true)
+
+      post :create, params: { user: { login: "citizen@consul.org", password: "12345678" }}
+
+      expect(response).to redirect_to account_path
+    end
+
+    it "redirects to welcome path when multitenancy_management_mode is disabled" do
+      allow(Rails.application.config).to receive(:multitenancy_management_mode).and_return(false)
+
+      post :create, params: { user: { login: "citizen@consul.org", password: "12345678" }}
+
+      expect(response).to redirect_to welcome_path
+    end
+  end
 end