Update JSDoc for types.ts for prometheus

The JSDoc has a mismatch with the actual default values of PrometheusExporter. It's false and not true

Author: Slawaq

experimental/packages/opentelemetry-exporter-prometheus/src/export/types.ts

@@ -29,7 +29,7 @@ export interface ExporterConfig {
 
   /**
    * Append timestamp to metrics
-   * @default true
+   * @default false
    */
   appendTimestamp?: boolean;