Pages: Add feature flag to disable deployment to legacy storage

Since we are transitioning to a new Pages deployment which does not
require extracting the ZIP file, we add a feature flag
(`skip_pages_deploy_to_legacy_storage`) that selectively disables this
extraction. This would help address
https://gitlab.com/gitlab-com/gl-infra/production/-/issues/4197.

app/services/projects/update_pages_service.rb

@@ -85,6 +85,8 @@ module Projects
       # so we can't really scope this feature flag by project or group
       return unless ::Settings.pages.local_store.enabled
 
+      return if Feature.enabled?(:skip_pages_deploy_to_legacy_storage, project, default_enabled: :yaml)
+
       # Create temporary directory in which we will extract the artifacts
       make_secure_tmp_dir(tmp_path) do |tmp_path|
         extract_archive!(artifacts_path, tmp_path)

changelogs/unreleased/sh-deploy-to-legacy-feature-flag.yml

+---
+title: 'Pages: Add feature flag to disable deployment to legacy storage'
+merge_request: 59298
+author:
+type: changed

config/feature_flags/development/skip_pages_deploy_to_legacy_storage.yml

+---
+name: skip_pages_deploy_to_legacy_storage
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/59298
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/327725
+milestone: '13.11'
+type: development
+group: group::release
+default_enabled: false

ee/spec/services/projects/update_pages_service_spec.rb

@@ -24,6 +24,7 @@ RSpec.describe Projects::UpdatePagesService do
                         .and_return(metadata)
 
       stub_licensed_features(pages_size_limit: true)
+      stub_feature_flags(skip_pages_deploy_to_legacy_storage: false)
     end
 
     it_behaves_like 'pages size limit is', 250.megabytes

spec/services/projects/update_pages_service_spec.rb

@@ -16,6 +16,7 @@ RSpec.describe Projects::UpdatePagesService do
   subject { described_class.new(project, build) }
 
   before do
+    stub_feature_flags(skip_pages_deploy_to_legacy_storage: false)
     project.legacy_remove_pages
   end
 
@@ -70,6 +71,16 @@ RSpec.describe Projects::UpdatePagesService do
         expect(File.exist?(File.join(project.pages_path, 'public', 'index.html'))).to eq(false)
       end
 
+      it "doesn't deploy to legacy storage if skip_pages_deploy_to_legacy_storage is enabled" do
+        allow(Settings.pages.local_store).to receive(:enabled).and_return(true)
+        stub_feature_flags(skip_pages_deploy_to_legacy_storage: true)
+
+        expect(execute).to eq(:success)
+        expect(project.pages_deployed?).to be_truthy
+
+        expect(File.exist?(File.join(project.pages_path, 'public', 'index.html'))).to eq(false)
+      end
+
       it 'creates pages_deployment and saves it in the metadata' do
         expect do
           expect(execute).to eq(:success)