Add empty state for Instance OAuth app page

Also update some of the table, button elements to use
Pajamas designs.

Changelog: changed

app/views/admin/applications/_delete_form.html.haml

+- submit_btn_css ||= 'gl-button btn btn-danger btn-danger-secondary btn-sm js-application-delete-button'
 
-- submit_btn_css ||= 'gl-button btn btn-danger btn-sm js-application-delete-button'
 %button{ class: submit_btn_css, data: { path: admin_application_path(application), name: application.name } }
   = _('Destroy')
-

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

-- page_title _("Applications")
+- page_title s_('AdminArea|Instance OAuth applications')
+
 %h3.page-title
-  = _('System OAuth applications')
+  = s_('AdminArea|Instance OAuth applications')
 %p.light
-  = _('System OAuth applications don\'t belong to any user and can only be managed by admins')
-%hr
-%p= link_to _('New application'), new_admin_application_path, class: 'gl-button btn btn-confirm'
-.table-responsive
-  %table.table
+  - docs_link_path = help_page_path('integration/oauth_provider')
+  - docs_link_start = '<a href="%{url}" target="_blank" rel="noopener noreferrer nofollow">'.html_safe % { url: docs_link_path }
+  = s_('AdminArea|Manage applications for your instance that can use GitLab as an %{docs_link_start}OAuth provider%{docs_link_end}.').html_safe % { docs_link_start: docs_link_start, docs_link_end: '</a>'.html_safe }
+
+- if @applications.empty?
+  %section.empty-state.gl-text-center.gl-display-flex.gl-flex-direction-column
+    .svg-content.svg-150
+      = image_tag 'illustrations/empty-state/empty-admin-apps.svg', class: 'gl-max-w-full'
+
+    .gl-max-w-full.gl-m-auto
+      %h1.h4.gl-font-size-h-display= s_('AdminArea|No applications found')
+      = link_to _('New application'), new_admin_application_path, class: 'btn gl-button btn-confirm'
+
+- else
+  %hr
+  %p= link_to _('New application'), new_admin_application_path, class: 'gl-button btn btn-confirm'
+
+  .table-responsive
+    %table.b-table.gl-table.gl-w-full{ role: 'table' }
       %thead
         %tr
           %th
@@ -23,7 +38,7 @@
           %th
       %tbody.oauth-applications
         - @applications.each do |application|
-        %tr{ :id => "application_#{application.id}" }
+          %tr{ id: "application_#{application.id}" }
             %td= link_to application.name, admin_application_path(application)
             %td= application.redirect_uri
             %td= @application_counts[application.id].to_i

locale/gitlab.pot

@@ -2495,6 +2495,9 @@ msgstr ""
 msgid "AdminArea|Included Free in license"
 msgstr ""
 
+msgid "AdminArea|Instance OAuth applications"
+msgstr ""
+
 msgid "AdminArea|Latest groups"
 msgstr ""
 
@@ -2507,6 +2510,9 @@ msgstr ""
 msgid "AdminArea|Maintainer"
 msgstr ""
 
+msgid "AdminArea|Manage applications for your instance that can use GitLab as an %{docs_link_start}OAuth provider%{docs_link_end}."
+msgstr ""
+
 msgid "AdminArea|Minimal access"
 msgstr ""
 
@@ -2519,6 +2525,9 @@ msgstr ""
 msgid "AdminArea|New user"
 msgstr ""
 
+msgid "AdminArea|No applications found"
+msgstr ""
+
 msgid "AdminArea|Owner"
 msgstr ""
 
@@ -36370,12 +36379,6 @@ msgstr ""
 msgid "System Info"
 msgstr ""
 
-msgid "System OAuth applications"
-msgstr ""
-
-msgid "System OAuth applications don't belong to any user and can only be managed by admins"
-msgstr ""
-
 msgid "System default (%{default})"
 msgstr ""