Allow ExCS admin to update starter project identifier

This modifies `Project::Update#update_project_attributes` so that if the
user has permission to update the project and the supplied identifier is
not blank, then the identifier is updated.

There are obviously some dangers associated with changing an existing
project's identifier, but I think it's still useful for an ExCS admin to
be able to do it.

Author: floehopper

lib/concepts/project/operations/update.rb

@@ -60,6 +60,12 @@ def update_project_attributes(response, update_hash, current_user)
         return if response.failure?
 
         response[:project].assign_attributes(update_hash.slice(:name, :instructions))
+
+        ability = Ability.new(current_user)
+        return unless ability.can?(:update, response[:project])
+        return if update_hash[:identifier].blank?
+
+        response[:project].identifier = update_hash[:identifier]
       end
 
       def update_component_attributes(response, update_hash)

spec/features/project/updating_a_project_spec.rb

@@ -104,6 +104,13 @@
       expect(response).to have_http_status(:success)
     end
 
+    it 'sets the project identifier to the specified value' do
+      put("/api/projects/#{project.identifier}?project_type=scratch", headers:, params:)
+      data = JSON.parse(response.body, symbolize_names: true)
+
+      expect(data[:identifier]).to eq('test-project')
+    end
+
     it 'sets the project name to the specified value' do
       put("/api/projects/#{project.identifier}?project_type=scratch", headers:, params:)
       data = JSON.parse(response.body, symbolize_names: true)