chore(playground): added example of echo interceptor

Author: manchenkoff

playground/app.config.ts

@@ -0,0 +1,12 @@
+export default defineAppConfig({
+  echo: {
+    interceptors: {
+      async onRequest(_app, ctx, logger) {
+        const tenant = 'random-string'
+
+        ctx.options.headers.set('X-Echo-Tenant', tenant)
+        logger.debug('Updated tenant header', tenant)
+      }
+    },
+  }
+})