Expose only status. ci_cd_status to status. Support abstract class.

app/controllers/projects/builds_controller.rb

app/controllers/projects/merge_requests_controller.rb

app/controllers/projects/pipelines_controller.rb

app/serializers/build_entity.rb

app/serializers/build_serializer.rb

app/serializers/pipeline_entity.rb

app/serializers/pipeline_serializer.rb

config/routes/project.rb

lib/gitlab/ci/status/core.rb

routes.txt