List S3 objects in atomic way

[daniel-y]

CompletableFuture<List<S3StreamObject>> streamObjectsFuture = metadataStore.listStreamObjects(streamId, startOffset, endOffset, limit);
CompletableFuture<List<S3WALObject>> walObjectsFuture = metadataStore.listWALObjects(streamId, startOffset, endOffset, limit);

return CompletableFuture.allOf(streamObjectsFuture, walObjectsFuture)
    .thenApplyAsync(v -> new Pair<>(streamObjectsFuture.join(), walObjectsFuture.join()));

Currently, we need two function calls to achieve a list s3 objects with two types.