Add deprecation warning for openSUSE Leap 15.1

Signed-off-by: Balasankar "Balu" C <balasankarc@autistici.org>

changelogs/unreleased/5688-opensuse-15-1-deprecation.yml

+---
+title: Add deprecation warning for openSUSE Leap 15.1
+merge_request: 4610
+author:
+type: deprecated

files/gitlab-cookbooks/package/libraries/omnibus_helper.rb

@@ -104,7 +104,8 @@ class OmnibusHelper
     {
       'raspbian-9' => 'GitLab 13.4',
       'debian-8' => 'GitLab 13.4',
-      'centos-6' => 'GitLab 13.7'
+      'centos-6' => 'GitLab 13.7',
+      'opensuseleap-15.1' => 'GitLab 13.7'
     }
   end