Cells: Fix cross joins in security/fetch_policy_approvers_service

Fix the cross joins in these files:

• ee/app/services/security/security_orchestration_policies/fetch_policy_approvers_service.rb:60:

Refer to the epic for more information about this. Feel free to:

1. Copy the epic description to this issue to helper the reviewers understand the problem.
2. Split this issue into different issues in case it was so much effort to
3. Ask for help and hints on #tenant-scale on how to fix cross joins

Implementation plan

We can probably solve this by using container.authorizable_members_with_parents.pluck(:user_id) and then fetching the users in a different query.

diff --git a/ee/app/services/security/security_orchestration_policies/fetch_policy_approvers_service.rb b/ee/app/services/security/security_orchestration_policies/fetch_policy_approvers_service.rb
index 28b6689f40e0..40aa13b6596a 100644
--- a/ee/app/services/security/security_orchestration_policies/fetch_policy_approvers_service.rb
+++ b/ee/app/services/security/security_orchestration_policies/fetch_policy_approvers_service.rb
@@ -50,17 +50,8 @@ def user_approvers(action)
 
       # rubocop: disable CodeReuse/ActiveRecord
       def authorizable_users_in_group_hierarchy_by_ids_or_usernames(user_ids, user_names)
-        User
-          .by_ids_or_usernames(user_ids, user_names)
-          .where(
-            container
-              .authorizable_members_with_parents
-              .merge(Member.where(Member.arel_table[:user_id].eq(User.arel_table[:id])), rewhere: true)
-              .select(1)
-              .arel
-              .exists
-          )
-          .allow_cross_joins_across_databases(url: "https://gitlab.com/gitlab-org/gitlab/-/issues/417460")
+        User.by_ids_or_usernames(user_ids, user_names)
+          .where(id: container.authorizable_members_with_parents.pluck(:user_id))
       end
       # rubocop: enable CodeReuse/ActiveRecord