feat: add a metric to monitor daily unique users (#19236)

#19234

backend/open_webui/utils/telemetry/metrics.py

@@ -99,6 +99,9 @@ def _build_meter_provider(resource: Resource) -> MeterProvider:
         View(
             instrument_name="webui.users.active",
         ),
+        View(
+            instrument_name="webui.users.active.today",
+        ),
     ]
 
     provider = MeterProvider(
@@ -159,6 +162,18 @@ def setup_metrics(app: FastAPI, resource: Resource) -> None:
         callbacks=[observe_active_users],
     )
 
+    def observe_users_active_today(
+        options: metrics.CallbackOptions,
+    ) -> Sequence[metrics.Observation]:
+        return [metrics.Observation(value=Users.get_num_users_active_today())]
+
+    meter.create_observable_gauge(
+        name="webui.users.active.today",
+        description="Number of users active since midnight today",
+        unit="users",
+        callbacks=[observe_users_active_today],
+    )
+
     # FastAPI middleware
     @app.middleware("http")
     async def _metrics_middleware(request: Request, call_next):