Skip Rack Attack rate limiting for container registry event API

As seen in https://gitlab.com/gitlab-org/gitlab/-/issues/327416,
previously Rack Attack throttled
`/api/v4/container_registry_event/events`, which then caused Rack Attack
to rate limit on other unauthenticated requests, such as fetches to
remote CI YAML files.

Since this is a trusted request from the Docker API, we can exempt this
from our rate limiting. We now skip the request if the path starts with
`/api/v4/container_registry_event/`.  We now skip the request if the
path starts with `/api/v4/container_registry_event/`.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/327416

changelogs/unreleased/sh-avoid-rate-limit-container-registry-events.yml

+---
+title: Skip Rack Attack rate limiting for container registry event API
+merge_request: 59085
+author:
+type: fixed

lib/gitlab/rack_attack/request.rb

@@ -34,12 +34,16 @@ module Gitlab
         path =~ %r{^/-/(health|liveness|readiness|metrics)}
       end
 
+      def container_registry_event?
+        path =~ %r{^/api/v\d+/container_registry_event/}
+      end
+
       def product_analytics_collector_request?
         path.start_with?('/-/collector/i')
       end
 
       def should_be_skipped?
-        api_internal_request? || health_check_request?
+        api_internal_request? || health_check_request? || container_registry_event?
       end
 
       def web_request?

spec/requests/rack_attack_global_spec.rb

@@ -143,6 +143,31 @@ RSpec.describe 'Rack Attack global throttles', :use_clean_rails_memory_store_cac
         end
       end
 
+      context 'when the request is to a container registry notification endpoint' do
+        let(:secret_token) { 'secret_token' }
+        let(:events) { [{ action: 'push' }] }
+        let(:registry_endpoint) { '/api/v4/container_registry_event/events' }
+        let(:registry_headers) { { 'Content-Type' => ::API::ContainerRegistryEvent::DOCKER_DISTRIBUTION_EVENTS_V1_JSON } }
+
+        before do
+          allow(Gitlab.config.registry).to receive(:notification_secret) { secret_token }
+
+          event = spy(:event)
+          allow(::ContainerRegistry::Event).to receive(:new).and_return(event)
+          allow(event).to receive(:supported?).and_return(true)
+        end
+
+        it 'does not throttle the requests' do
+          (1 + requests_per_period).times do
+            post registry_endpoint,
+                 params: { events: events }.to_json,
+                 headers: registry_headers.merge('Authorization' => secret_token)
+
+            expect(response).to have_gitlab_http_status(:ok)
+          end
+        end
+      end
+
       it 'logs RackAttack info into structured logs' do
         requests_per_period.times do
           get url_that_does_not_require_authentication