Fix references to Administrator role and other improvements

app/views/admin/users/_access_levels.html.haml

doc/.vale/gitlab/SubstitutionWarning.yml

doc/.vale/gitlab/Substitutions.yml

doc/administration/auditor_users.md

doc/administration/auth/ldap/ldap-troubleshooting.md

doc/administration/monitoring/performance/performance_bar.md

doc/administration/monitoring/prometheus/gitlab_metrics.md

...dministration/troubleshooting/gitlab_rails_cheat_sheet.md

doc/api/deploy_keys.md

doc/api/deploy_tokens.md

doc/api/groups.md

doc/api/instance_clusters.md

doc/api/pages.md

doc/api/pages_domains.md

doc/api/plan_limits.md

doc/api/project_snippets.md

doc/api/runners.md

doc/api/users.md

doc/ci/pipelines/job_artifacts.md

doc/ci/services/index.md