[EE] Resolve "GitLab Project export should use object storage"

app/controllers/projects_controller.rb

app/models/import_export_upload.rb

app/models/project.rb

app/services/import_export_clean_up_service.rb

app/uploaders/import_export_uploader.rb

app/views/projects/_export.html.haml

...46246-gitlab-project-export-should-use-object-storage.yml

db/migrate/20180625113853_create_import_export_uploads.rb

db/schema.rb

doc/administration/raketasks/project_import_export.md

lib/api/project_export.rb

lib/gitlab/import_export.rb

...ort/after_export_strategies/base_after_export_strategy.rb

...ort_export/after_export_strategies/web_upload_strategy.rb

lib/gitlab/import_export/saver.rb

spec/controllers/projects_controller_spec.rb

spec/factories/import_export_uploads.rb

spec/factories/projects.rb

spec/features/projects/import_export/export_file_spec.rb

...ures/projects/import_export/namespace_export_file_spec.rb