Merge branch 'experimentation-cookie-domain' into 'master'

Set experimentation cookie for GitLab domain only

Closes #36741

See merge request gitlab-org/gitlab!30303

changelogs/unreleased/experimentation-cookie-domain.yml

+---
+title: Set experiementation cookie for GitLab domain only
+merge_request:
+author:
+type: fixed

lib/gitlab/experimentation.rb

@@ -66,7 +66,6 @@ module Gitlab
 
         cookies.permanent.signed[:experimentation_subject_id] = {
           value: SecureRandom.uuid,
-          domain: :all,
           secure: ::Gitlab.config.gitlab.https,
           httponly: true
         }