Rename index files for Hugo migration

app/assets/javascripts/usage_quotas/storage/constants.js

app/views/admin/application_settings/_pages.html.haml

...application_settings/_silent_mode_settings_form.html.haml

app/views/admin/dashboard/index.html.haml

app/views/shared/_silent_mode_banner.html.haml

app/views/shared/packages/_no_packages.html.haml

doc/administration/audit_event_streaming/_index.md

doc/administration/auth/_index.md

doc/administration/auth/ldap/_index.md

doc/administration/auth/ldap/google_secure_ldap.md

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

doc/administration/auth/ldap/ldap_synchronization.md

doc/administration/backup_restore/_index.md

doc/administration/backup_restore/backup_cli.md

doc/administration/backup_restore/backup_gitlab.md

doc/administration/backup_restore/migrate_to_new_server.md

doc/administration/cicd/job_artifacts.md

doc/administration/configure.md

doc/administration/dedicated/architecture.md

doc/administration/encrypted_configuration.md