Add API get handler for usage data queries

Add specs for the API calls

config/feature_flags/ops/usage_data_queries_api.yml

+---
+name: usage_data_queries_api
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57016
+rollout_issue_url: 
+milestone: '13.11'
+type: ops
+group: group::product intelligence
+default_enabled: false

lib/api/api.rb

@@ -293,6 +293,7 @@ module API
       mount ::API::Triggers
       mount ::API::Unleash
       mount ::API::UsageData
+      mount ::API::UsageDataQueries
       mount ::API::UserCounts
       mount ::API::Users
       mount ::API::Variables

lib/api/usage_data_queries.rb

+# frozen_string_literal: true
+
+module API
+  class UsageDataQueries < ::API::Base
+    before { authenticated_as_admin! }
+
+    feature_category :usage_ping
+
+    namespace 'usage_data' do
+      before do
+        not_found! unless Feature.enabled?(:usage_data_queries_api, default_enabled: false, type: :ops)
+      end
+
+      desc 'Get raw SQL queries for usage data SQL metrics' do
+        detail 'This feature was introduced in GitLab 13.11.'
+      end
+
+      get 'queries' do
+        Gitlab::QueryLimiting.disable!('https://gitlab.com/gitlab-org/gitlab/-/issues/325534')
+
+        queries = Gitlab::UsageDataQueries.uncached_data
+
+        present queries
+      end
+    end
+  end
+end

spec/requests/api/usage_data_queries_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe API::UsageDataQueries do
+  include UsageDataHelpers
+
+  let_it_be(:admin) { create(:user, admin: true) }
+  let_it_be(:user) { create(:user) }
+
+  before do
+    stub_usage_data_connections
+  end
+
+  describe 'GET /usage_data/usage_data_queries' do
+    let(:endpoint) { '/usage_data/queries' }
+
+    context 'with authentication' do
+      before do
+        stub_feature_flags(usage_data_queries_api: true)
+      end
+
+      it 'returns queries if user is admin' do
+        get api(endpoint, admin)
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(json_response['active_user_count']).to start_with('SELECT COUNT("users"."id") FROM "users"')
+      end
+
+      it 'returns forbidden if user is not admin' do
+        get api(endpoint, user)
+
+        expect(response).to have_gitlab_http_status(:forbidden)
+      end
+    end
+
+    context 'without authentication' do
+      before do
+        stub_feature_flags(usage_data_queries_api: true)
+      end
+
+      it 'returns unauthorized' do
+        get api(endpoint)
+
+        expect(response).to have_gitlab_http_status(:unauthorized)
+      end
+    end
+
+    context 'when feature_flag is disabled' do
+      before do
+        stub_feature_flags(usage_data_queries_api: false)
+      end
+
+      it 'returns not_found for admin' do
+        get api(endpoint, admin)
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+
+      it 'returns forbidden for non-admin' do
+        get api(endpoint, user)
+
+        expect(response).to have_gitlab_http_status(:forbidden)
+      end
+    end
+  end
+end