docs: update root health docs

Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

docs/backend-system/core-services/root-health.md

@@ -1,38 +1,40 @@
 ---
-id: health
-title: Heath Service
+id: root-health
+title: Root Health Service
 sidebar_label: Health
 description: Documentation for the Health service
 ---
 
-The Health service provides some health check endpoints for the plugins. By default, it attaches `/.backstage/health/v1/readiness` and `/.backstage/health/v1/liveness` endpoints to the backend server, which return a JSON object with the status of the backend services.
+The Root Health service provides some health check endpoints for the backend. By default, the `rootHttpRouter` exposes a `/.backstage/health/v1/readiness` and `/.backstage/health/v1/liveness` endpoints, which return a JSON object with the status of the backend services according the implementation of the Root Health Service.
 
 ## Configuring the service
 
-The following example is how you can override the health service to add custom endpoints.
+The following example is how you can override the health service implementation.
 
 ```ts
-import { coreServices } from '@backstage/backend-plugin-api';
+import { RootHealthService, coreServices } from '@backstage/backend-plugin-api';
 import { WinstonLogger } from '@backstage/backend-app-api';
 
 const backend = createBackend();
 
+class MyRootHealthService implements RootHealthService {
+  async getLiveness(): Promise<{ status: number; payload?: any }> {
+    // provide your own implementation
+    return { status: 200, payload: { status: 'ok' } };
+  }
+
+  async getReadiness(): Promise<{ status: number; payload?: any }> {
+    // provide your own implementation
+    return { status: 200, payload: { status: 'ok' } };
+  }
+}
+
 backend.add(
   createServiceFactory({
-    service: coreServices.health,
-    deps: {
-      rootHttpRouter: coreServices.rootHttpRouter,
-    },
-    async factory({ rootHttpRouter }) {
-      rootHttpRouter.get('.backstage/health/v1/readiness', async (req, res) => {
-        res.json({ status: 'ok' });
-      });
-
-      rootHttpRouter.get('.backstage/health/v1/liveness', async (req, res) => {
-        res.json({ status: 'ok' });
-      });
-
-      return {};
+    service: coreServices.rootHealth,
+    deps: {},
+    async factory({}) {
+      return new MyRootHealthService();
     },
   }),
 );