Added deprecation notice to cluster creation pages

As we already deprecated the certificate-based cluster connection,
we add a deprecation notice to cluster creation and connection pages.

Changelog: added

app/views/clusters/clusters/_deprecation_alert.html.haml

+.gl-alert.gl-alert-warning.gl-mt-6{ role: 'alert' }
+  = sprite_icon('warning', css_class: "gl-alert-icon gl-alert-icon-no-title gl-icon")
+  .gl-alert-body
+    - link_start = '<a href="%{url}" target="_blank" rel="noopener noreferrer">'.html_safe
+    - issue_link_start = link_start % { url: 'https://gitlab.com/gitlab-org/configure/general/-/issues/199' }
+    - docs_link_start = link_start % { url: help_page_path('user/clusters/agent/index.md') }
+    - link_end = '</a>'.html_safe
+    = s_('ClusterIntegration|The certificate-based cluster connection method has been %{issue_link_start}deprecated%{issue_link_end}. We recommend using %{docs_link_start}the GitLab agent for Kubernetes%{docs_link_end} instead.').html_safe % { docs_link_start: docs_link_start, docs_link_end: link_end, issue_link_start: issue_link_start, issue_link_end: link_end }

app/views/clusters/clusters/connect.html.haml

@@ -3,6 +3,8 @@
 - breadcrumb_title _('Connect a cluster')
 - page_title _('Connect a Kubernetes Cluster')
 
+= render 'deprecation_alert'
+
 .gl-md-display-flex.gl-mt-3
   .gl-w-quarter.gl-xs-w-full.gl-flex-shrink-0.gl-md-mr-5
     = render 'sidebar', is_connect_page: true

app/views/clusters/clusters/new.html.haml

@@ -4,6 +4,8 @@
 - page_title _('Create a Kubernetes cluster')
 - provider = params[:provider]
 
+= render 'deprecation_alert'
+
 = render_gcp_signup_offer
 
 .gl-md-display-flex.gl-mt-3

locale/gitlab.pot

@@ -8763,6 +8763,9 @@ msgstr ""
 msgid "ClusterIntegration|The URL used to access the Kubernetes API."
 msgstr ""
 
+msgid "ClusterIntegration|The certificate-based cluster connection method has been %{issue_link_start}deprecated%{issue_link_end}. We recommend using %{docs_link_start}the GitLab agent for Kubernetes%{docs_link_end} instead."
+msgstr ""
+
 msgid "ClusterIntegration|The certificate-based method to connect clusters to GitLab was %{linkStart}deprecated%{linkEnd} in GitLab 14.5."
 msgstr ""