fix: Convert undefined values to null in LlamaCloud filters (#1319)

.changeset/selfish-frogs-lie.md

packages/llamaindex/src/cloud/LLamaCloudFileService.ts

packages/llamaindex/src/cloud/LlamaCloudIndex.ts

packages/llamaindex/src/cloud/LlamaCloudRetriever.ts

packages/llamaindex/src/cloud/utils.ts