Order GitLab CI keywords

Order the keywords in .gitlab-ci.yml consistently. Global keywords come first, in the order include, stages, variables, workflow and default, followed by the jobs in their original order. Within default and each job, keywords follow the order in which they take effect: inheritance, scheduling, execution environment, scripts and finally outputs such as artifacts. Unrecognized keys keep their relative order after the recognized ones. A mapping is left unchanged when reordering would place a YAML alias before its anchor.