Reorganized runner content to bring SaaS shared runners to main page

app/views/shared/runners/_runner_type_alert.html.haml

doc/administration/index.md

doc/ci/caching/index.md

doc/ci/docker/using_docker_build.md

doc/ci/docker/using_kaniko.md

doc/ci/environments/deployment_safety.md

doc/ci/environments/index.md

doc/ci/environments/protected_environments.md

doc/ci/git_submodules.md

doc/ci/interactive_web_terminal/index.md

doc/ci/large_repositories/index.md

doc/ci/migration/jenkins.md

doc/ci/pipelines/settings.md

doc/ci/quick_start/index.md

doc/ci/runners/README.md

doc/ci/runners/configure_runners.md

doc/ci/runners/runners_scope.md

doc/ci/yaml/README.md

doc/development/documentation/index.md

doc/development/pipelines.md