Merge branch 'feature/gb/persist-pipeline-stages' into 'master'

app/controllers/projects/pipelines_controller.rb

app/models/ci/legacy_stage.rb

app/models/ci/pipeline.rb

app/models/ci/stage.rb

app/models/commit_status.rb

app/serializers/pipeline_details_entity.rb

app/services/ci/create_pipeline_builds_service.rb

app/services/ci/create_pipeline_service.rb

app/services/ci/create_pipeline_stages_service.rb

app/services/ci/retry_build_service.rb

app/views/projects/commit/_commit_box.html.haml

app/views/projects/jobs/_sidebar.html.haml

app/views/projects/pipelines/_with_tabs.html.haml

app/views/shared/_mini_pipeline_graph.html.haml

changelogs/unreleased/feature-gb-persist-pipeline-stages.yml

lib/ci/gitlab_ci_yaml_processor.rb

lib/gitlab/ci/stage/seed.rb

lib/gitlab/data_builder/pipeline.rb

lib/gitlab/import_export/import_export.yml

lib/gitlab/import_export/relation_factory.rb