fix: cache thumbnail in display set (#4782)

platform/core/src/types/DisplaySet.ts

@@ -12,6 +12,12 @@ export type DisplaySet = {
   Modality?: string;
   imageIds?: string[];
   images?: unknown[];
+
+  // Details about how to display:
+  /** A URL that can be used to display the thumbnail.  Typically a data url */
+  thumbnailSrc?: string;
+  /** A fetch method to get the thumbnail */
+  getThumbnailSrc?(imageId?: string): Promise<string>;
   SeriesDate?: string;
   SeriesTime?: string;
   instance?: InstanceMetadata;