Rename index.md to _index.md for compatibility with docs-gitlab-com

...ascripts/ci/pipelines_page/components/pipeline_labels.vue

...avascripts/repository/components/commit_changes_modal.vue

app/helpers/clusters_helper.rb

app/helpers/mirror_helper.rb

app/helpers/projects_helper.rb

app/presenters/projects/security/configuration_presenter.rb

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

app/views/admin/groups/show.html.haml

app/views/admin/projects/show.html.haml

app/views/groups/_group_admin_settings.html.haml

app/views/groups/settings/_lfs.html.haml

app/views/groups/settings/ci_cd/_auto_devops_form.html.haml

app/views/groups/settings/ci_cd/show.html.haml

app/views/notify/autodevops_disabled_email.html.haml

app/views/projects/_lfs_misconfiguration_banner.html.haml

app/views/projects/empty.html.haml

app/views/projects/settings/ci_cd/_autodevops_form.html.haml

app/views/projects/settings/ci_cd/show.html.haml

app/views/shared/_auto_devops_callout.html.haml

...s/shared/_auto_devops_implicitly_enabled_banner.html.haml