Lots of spelling fixes

doc/development/ai_architecture.md

doc/development/ai_features/index.md

doc/development/avoiding_required_stops.md

doc/development/backend/ruby_style_guide.md

doc/development/code_suggestions/index.md

doc/development/contributing/index.md

doc/development/database/multiple_databases.md

doc/development/database/understanding_explain_plans.md

doc/development/documentation/styleguide/index.md

doc/development/documentation/testing.md

doc/development/fe_guide/frontend_goals.md

doc/development/fe_guide/getting_started.md

doc/development/fe_guide/index.md

doc/development/gems.md

...ent/gitlab_flavored_markdown/specification_guide/index.md

doc/development/gitlab_shell/index.md

...internal_analytics/internal_event_tracking/quick_start.md

...ment/internal_analytics/service_ping/review_guidelines.md

doc/development/licensing.md

doc/development/migration_style_guide.md