[FSSDK-11197] EventTags type fix v6

Author: junaed-optimizely

lib/shared_types.ts

@@ -92,6 +92,7 @@ export type EventTags = {
   revenue?: string | number | null;
   value?: string | number | null;
   $opt_event_properties?: Record<string, unknown>;
+  [key: string]: unknown;
 };
 
 export interface UserProfileService {