TimelineDataDescription to accept any properties

Summary: DataInspector can use `any` value to inspect. Lift the constraint from TimelineDataDescription as ultimately is not necessary i.e. the right inspector will be used based on the type of properties.

Reviewed By: antonk52

Differential Revision: D44572963

fbshipit-source-id: ad8a257020c90e18468e905f2beda44c2ee06368

desktop/flipper-plugin/src/ui/data-inspector/TimelineDataDescription.tsx

@@ -19,7 +19,7 @@ type TimePoint = {
   display: string;
   color: string;
   key: string;
-  properties?: {[key: string]: string};
+  properties?: any;
 };
 
 type Timeline = {