Document stages and jobs.

docs/files/screenshots/pipeline_check4updates.png

docs/files/screenshots/pipeline_deploy.png

docs/files/screenshots/pipeline_executebuild.png

docs/files/screenshots/pipeline_lakedrops_build.png

docs/files/screenshots/pipeline_lakedrops_deploy.png

docs/files/screenshots/pipeline_publish_release.png

docs/gitlab/drupal/index.md

docs/gitlab/pipelines/index.md

mkdocs.yml