Check application settings instead of Gitlab.com?

- Checking application settings is more extensible. It allows the same
  code to work in other SaaS offerings (like JH).
- It also makes it easier to test locally, since we can simply modify
  the application setting value in the local database, instead of
  modifying the Gitlab.com? method.
- See https://gitlab.com/gitlab-org/gitlab/-/issues/225101 for more
  details.

ee/app/models/gitlab_subscriptions/upcoming_reconciliation.rb

@@ -4,10 +4,12 @@ module GitlabSubscriptions
   class UpcomingReconciliation < ApplicationRecord
     belongs_to :namespace, inverse_of: :upcoming_reconciliation, optional: true
 
-    validates :namespace, uniqueness: true, presence: { if: proc { ::Gitlab.com? } }
+    # Validate presence of namespace_id if this is running on a GitLab instance
+    # that has paid namespaces.
+    validates :namespace, uniqueness: true, presence: { if: proc { ::Gitlab::CurrentSettings.should_check_namespace_plan? } }
 
     def self.next(namespace_id = nil)
-      if ::Gitlab.com?
+      if ::Gitlab::CurrentSettings.should_check_namespace_plan?
         return unless namespace_id
 
         self.find_by(namespace_id: namespace_id)

ee/spec/helpers/gitlab_subscriptions/upcoming_reconciliation_helper_spec.rb

@@ -19,7 +19,7 @@ RSpec.describe GitlabSubscriptions::UpcomingReconciliationHelper do
     end
 
     before do
-      allow(::Gitlab).to receive(:com?).and_return(true)
+      stub_application_setting(check_namespace_plan: true)
     end
 
     it 'returns true and reconciliation date' do
@@ -51,9 +51,9 @@ RSpec.describe GitlabSubscriptions::UpcomingReconciliationHelper do
       end
     end
 
-    context 'when not gitlab.com' do
+    context 'when instance does not have paid namespaces (ex: self managed instance)' do
       it 'returns false and empty hash' do
-        allow(::Gitlab).to receive(:com?).and_return(false)
+        stub_application_setting(check_namespace_plan: false)
 
         expect(helper.display_upcoming_reconciliation_alert?(namespace)).to eq(false)
         expect(helper.upcoming_reconciliation_hash(namespace)).to eq({})
@@ -119,9 +119,9 @@ RSpec.describe GitlabSubscriptions::UpcomingReconciliationHelper do
       end
     end
 
-    context 'when gitlab.com' do
+    context 'when instance has paid namespaces (ex: gitlab.com)' do
       it 'returns false and empty hash' do
-        allow(::Gitlab).to receive(:com?).and_return(true)
+        stub_application_setting(check_namespace_plan: true)
         enable_admin_mode!(user)
 
         expect(helper.display_upcoming_reconciliation_alert?).to eq(false)

ee/spec/models/gitlab_subscriptions/upcoming_reconciliation_spec.rb

@@ -22,15 +22,15 @@ RSpec.describe GitlabSubscriptions::UpcomingReconciliation do
       )
     end
 
-    context 'when gitlab.com' do
+    context 'when instance has paid namespaces (ex: gitlab.com)' do
       before do
-        allow(Gitlab).to receive(:com?).and_return(true)
+        stub_application_setting(check_namespace_plan: true)
       end
 
       it { is_expected.to validate_presence_of(:namespace) }
     end
 
-    context 'when not gitlab.com' do
+    context 'when namespaces are not paid (ex: self managed instance)' do
       it { is_expected.not_to validate_presence_of(:namespace) }
     end
   end
@@ -78,13 +78,13 @@ RSpec.describe GitlabSubscriptions::UpcomingReconciliation do
       end
     end
 
-    context 'when SaaS' do
+    context 'when instance has paid namespaces (ex: gitlab.com)' do
       let_it_be(:upcoming_reconciliation) { create(:upcoming_reconciliation, :saas) }
 
       let(:namespace_id) { upcoming_reconciliation.namespace_id }
 
       before do
-        allow(::Gitlab).to receive(:com?).and_return(true)
+        stub_application_setting(check_namespace_plan: true)
       end
 
       it 'returns row for given namespace' do