feat(config, usage): add usage-statistics-enabled option and dynamic toggling

- Introduced `usage-statistics-enabled` configuration to control in-memory usage aggregation.
- Updated API to include handlers for managing `usage-statistics-enabled` and `logging-to-file` options.
- Enhanced `watcher` to log changes to both configurations dynamically.
- Updated documentation and examples to reflect new configuration options.

cmd/server/main.go

@@ -14,6 +14,7 @@ import (
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/logging"
 	_ "github.com/router-for-me/CLIProxyAPI/v6/internal/translator"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/usage"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/util"
 	sdkAuth "github.com/router-for-me/CLIProxyAPI/v6/sdk/auth"
 	log "github.com/sirupsen/logrus"
@@ -111,6 +112,7 @@ func main() {
 	if err != nil {
 		log.Fatalf("failed to load config: %v", err)
 	}
+	usage.SetStatisticsEnabled(cfg.UsageStatisticsEnabled)
 
 	if err = logging.ConfigureLogOutput(cfg.LoggingToFile); err != nil {
 		log.Fatalf("failed to configure log output: %v", err)