Add NGWAF metrics

apiadded

Historical Stats responses now include the following new metrics: ngwaf_requests_total_count, ngwaf_requests_unknown_count, ngwaf_requests_allowed_count, ngwaf_requests_logged_count, ngwaf_requests_blocked_count, ngwaf_requests_timeout_count, and ngwaf_requests_challenged_count.

Prior change: Added not_before and not_after filters to GET bulk tls certs endpoint

Following change: Fix type of 'priority' field on Condition, Header, and Snippet