Implement extra domains and save pages configuration

app/controllers/projects/pages_controller.rb

app/helpers/projects_helper.rb

app/models/pages_domain.rb

app/services/projects/update_pages_configuration_service.rb

app/views/projects/pages/_access.html.haml

app/views/projects/pages/_destroy.haml

app/views/projects/pages/_form.html.haml

app/views/projects/pages/_list.html.haml

app/views/projects/pages/_no_domains.html.haml

app/views/projects/pages/_remove_certificate.html.haml

app/views/projects/pages/_upload_certificate.html.haml

app/views/projects/pages/index.html.haml

app/views/projects/pages/new.html.haml

app/views/projects/pages/show.html.haml

config/gitlab.yml.example

config/initializers/1_settings.rb

config/routes/project.rb