fix missing metrics endpoint

see vllm-project/vllm#6463

Author: dtrifiro

src/vllm_tgis_adapter/__main__.py

@@ -75,11 +75,13 @@
 
 router = APIRouter()
 
-# Add prometheus asgi middleware to route /metrics requests
-route = Mount("/metrics", make_asgi_app())
-# Workaround for 307 Redirect for /metrics
-route.path_regex = re.compile("^/metrics(?P<path>.*)$")
-router.routes.append(route)
+
+def mount_metrics(app: fastapi.FastAPI) -> None:
+    # Add prometheus asgi middleware to route /metrics requests
+    metrics_route = Mount("/metrics", make_asgi_app())
+    # Workaround for 307 Redirect for /metrics
+    metrics_route.path_regex = re.compile("^/metrics(?P<path>.*)$")
+    app.routes.append(metrics_route)
 
 
 @router.get("/health")
@@ -188,6 +190,8 @@ async def _force_log():  # noqa: ANN202
     app.include_router(router)
     app.root_path = args.root_path
 
+    mount_metrics(app)
+
     app.add_middleware(
         CORSMiddleware,
         allow_origins=args.allowed_origins,