feat(metrics): Implement MetricsService (#32977)

* feat: add MetricsService alpha release

Introduces MetricsService as a new @alpha core service wrapping
@opentelemetry/api. Includes migration of existing catalog metrics
to use the new service.

Signed-off-by: benjdlambert <ben@blam.sh>

* chore: duplicate otel types, add plugin-scoped factory and tests

Signed-off-by: benjdlambert <ben@blam.sh>

* chore: update BEP-0012 metrics service design

Signed-off-by: Kurt King <kurtaking@gmail.com>

* chore: address PR feedback from freben and rugvip

Rename instrument types with MetricsService prefix for namespace
clarity, move config to backend.metrics.plugin.{pluginId}, add
config.d.ts schema, and improve factory test assertions.

Signed-off-by: benjdlambert <ben@blam.sh>

---------

Signed-off-by: benjdlambert <ben@blam.sh>
Signed-off-by: Kurt King <kurtaking@gmail.com>
Co-authored-by: Kurt King <kurtaking@gmail.com>

packages/backend-defaults/config.d.ts

@@ -1127,6 +1127,36 @@ export interface Config {
       headers?: { [name: string]: string };
     };
 
+    /**
+     * Options for the metrics service.
+     */
+    metrics?: {
+      /**
+       * Plugin-specific metrics configuration. Each plugin can override meter metadata.
+       */
+      plugin?: {
+        [pluginId: string]: {
+          /**
+           * Meter configuration for this plugin.
+           */
+          meter?: {
+            /**
+             * Custom meter name. If not set, defaults to backstage-plugin-{pluginId}.
+             */
+            name?: string;
+            /**
+             * Version for the meter.
+             */
+            version?: string;
+            /**
+             * Schema URL for the meter.
+             */
+            schemaUrl?: string;
+          };
+        };
+      };
+    };
+
     /**
      * Options to configure the default RootLoggerService.
      */