Add gl-button class to buttons

This work is done as part of Pajamas Migration

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

@@ -3,7 +3,7 @@
     .settings-header
       %h4
         = _('Package Registry')
-      %button.btn.btn-default.js-settings-toggle{ type: 'button' }
+      %button.btn.gl-button.btn-default.js-settings-toggle{ type: 'button' }
         = expanded_by_default? ? _('Collapse') : _('Expand')
       %p
         = _("Settings related to the use and experience of using GitLab's Package Registry.")

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

@@ -17,7 +17,7 @@
   .settings-header
     %h4
       = _('Continuous Integration and Deployment')
-    %button.btn.btn-default.js-settings-toggle{ type: 'button' }
+    %button.btn.gl-button.btn-default.js-settings-toggle{ type: 'button' }
       = expanded_by_default? ? _('Collapse') : _('Expand')
     %p
       = _('Auto DevOps, runners and job artifacts')
@@ -33,7 +33,7 @@
     .settings-header
       %h4
         = _('Container Registry')
-      %button.btn.btn-default.js-settings-toggle{ type: 'button' }
+      %button.btn.gl-button.btn-default.js-settings-toggle{ type: 'button' }
         = expanded_by_default? ? _('Collapse') : _('Expand')
       %p
         = _('Various container registry settings.')

ee/app/views/admin/application_settings/_required_instance_ci_setting.html.haml

@@ -4,7 +4,7 @@
   .settings-header
     %h4
       = s_('AdminSettings|Required pipeline configuration')
-    %button.btn.btn-default.js-settings-toggle{ type: 'button' }
+    %button.btn.gl-button.btn-default.js-settings-toggle{ type: 'button' }
       = expanded ? _('Collapse') : _('Expand')
     %p
       - config_link_start = '<a href="%{url}">'.html_safe % { url: help_page_path('ci/yaml/README') }