Work Items list [BE] - Add "Email a New Work Item to This Project" Feature

Provide an option for users to email new work items directly to a specified group.

Appears on the bottom of the lists view. Documentation: https://docs.gitlab.com/user/project/issues/create_issues/#by-sending-an-email

On the frontend, this "Email a New Issue to This Project" is only shown on the project issues list when project.new_issuable_address(current_user, 'issue') returns a value from the backend.

For group-level work items, we should update the backend to work for groups too. Focus on this work should be on projects.