Add feature flag to disable db-writes on git-http

This adds the disable_git_http_fetch_writes feature flag. It allows
diabling some non-essential writes during git fetches hopefully
improving the apdex of some of the git endpoints.

app/controllers/repositories/git_http_controller.rb

@@ -78,6 +78,8 @@ module Repositories
     def update_fetch_statistics
       return unless project
       return if Gitlab::Database.read_only?
+      return if Feature.enabled?(:disable_git_http_fetch_writes)
+
       return unless repo_type.project?
 
       OnboardingProgressService.new(project.namespace).execute(action: :git_read)

config/feature_flags/development/disable_git_http_fetch_writes.yml

+---
+name: disable_git_http_fetch_writes
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/54322
+rollout_issue_url: https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/883
+milestone: '13.9'
+type: development
+group: group::source code
+default_enabled: false

spec/controllers/repositories/git_http_controller_spec.rb

@@ -36,7 +36,7 @@ RSpec.describe Repositories::GitHttpController do
 
         context 'when project_statistics_sync feature flag is disabled' do
           before do
-            stub_feature_flags(project_statistics_sync: false)
+            stub_feature_flags(project_statistics_sync: false, disable_git_http_fetch_writes: false)
           end
 
           it 'updates project statistics async for projects' do
@@ -47,6 +47,8 @@ RSpec.describe Repositories::GitHttpController do
         end
 
         it 'updates project statistics sync for projects' do
+          stub_feature_flags(disable_git_http_fetch_writes: false)
+
           expect { send_request }.to change {
             Projects::DailyStatisticsFinder.new(container).total_fetch_count
           }.from(0).to(1)
@@ -56,6 +58,29 @@ RSpec.describe Repositories::GitHttpController do
           let(:namespace) { project.namespace }
 
           subject { send_request }
+
+          before do
+            stub_feature_flags(disable_git_http_fetch_writes: false)
+          end
+        end
+
+        context 'when disable_git_http_fetch_writes is enabled' do
+          before do
+            stub_feature_flags(disable_git_http_fetch_writes: true)
+          end
+
+          it 'does not increment statistics' do
+            expect(Projects::FetchStatisticsIncrementService).not_to receive(:new)
+            expect(ProjectDailyStatisticsWorker).not_to receive(:perform_async)
+
+            send_request
+          end
+
+          it 'does not record onboarding progress' do
+            expect(OnboardingProgressService).not_to receive(:new)
+
+            send_request
+          end
         end
       end
     end