Add metrics logging for chat completion requests (#195)

- Add token and performance metrics  for v1/chat/completions 
- Add Activity Page in UI
- Add /api/metrics endpoint

Contributed by @g2mt

proxy/config_windows_test.go

@@ -193,6 +193,7 @@ groups:
 			},
 		},
 		HealthCheckTimeout: 15,
+		MetricsMaxInMemory: 1000,
 		Profiles: map[string][]string{
 			"test": {"model1", "model2"},
 		},