mediawikI: Add a way to view opcache/apcu stats

This is from wikimedias puppet repo [0] with minor tweeks to conform to
how we do things.

[0] https://github.com/wikimedia/operations-puppet/blob/bd7cbb36d87e147da028c3c51b583f93f5851957/modules/profile/manifests/mediawiki/php/monitoring.pp

modules/mediawiki/files/php/admin/index.php

@@ -0,0 +1,65 @@
+<?php
+/*
+
+Admin cli interface for php-fpm. It supports a /metrics endpoint where we expose data
+in a format prometheus likes.
+*/
+require('lib.php');
+
+$usage = <<<'EOD'
+Supported urls:
+
+  /metrics         Metrics about APCu and OPcache usage
+  /apcu-info       Show basic APCu stats
+  /apcu-meta       Dump meta information for all objects in APCu to /tmp/apcu_dump_meta
+  /apcu-free       Clear all data from APCu
+  /apcu-frag       APCu fragmentation percentage
+  /opcache-info    Show basic opcache stats
+  /opcache-meta    Dump meta information for all objects in opcache to /tmp/opcache_dump_meta
+  /opcache-free    Clear all data from opcache
+  /ini-get         Get the ini values for the running daemon. Add a key parameter if you want just one.
+
+EOD;
+
+ob_start();
+
+switch ($_SERVER['SCRIPT_NAME']) {
+	case '/metrics':
+		# This will make requests to the other php admin ports for /local-metrics, and combine them all
+		# in a single output.
+		show_all_prometheus_metrics();
+		break;
+	case '/local-metrics':
+		show_prometheus_metrics();
+		break;
+	case '/apcu-info':
+		show_apcu_info();
+		break;
+	case '/apcu-meta':
+		dump_apcu_full();
+		break;
+	case '/apcu-free':
+		// this is an administrative action
+		clear_apcu();
+		break;
+	case '/apcu-frag':
+		show_apcu_frag();
+		break;
+	case '/opcache-info':
+		show_opcache_info();
+		break;
+	case '/opcache-meta':
+		dump_opcache_meta();
+		break;
+	case '/opcache-free':
+		clear_opcache();
+		break;
+	case '/ini-get':
+		ini_value();
+		break;
+	default:
+		header("Content-Type: text/plain");
+		echo $usage;
+}
+
+ob_flush();