Rename index files to settings

This change renames runner configuration files to "settings" instead of
"index" to free up that name, so an index page can be added in the
future.

No user facing changes are expected.

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

@@ -34,7 +34,7 @@
       = _("Runners are processes that pick up and execute CI/CD jobs for GitLab.")
       = link_to s_('How do I configure runners?'), help_page_path('ci/runners/index'), target: '_blank', rel: 'noopener noreferrer'
   .settings-content
-    = render 'groups/runners/index'
+    = render 'groups/runners/settings'
 
 %section.settings#auto-devops-settings.no-animate{ class: ('expanded' if expanded) }
   .settings-header

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

@@ -43,7 +43,7 @@
       = _("Runners are processes that pick up and execute CI/CD jobs for GitLab.")
       = link_to s_('How do I configure runners?'), help_page_path('ci/runners/index'), target: '_blank', rel: 'noopener noreferrer'
   .settings-content
-    = render 'projects/runners/index'
+    = render 'projects/runners/settings'
 
 - if Gitlab::CurrentSettings.current_application_settings.keep_latest_artifact?
   %section.settings.no-animate#js-artifacts-settings{ class: ('expanded' if expanded) }