Added a sample integration for LLM models in huggingface

[vikashg]

I have added a sample application for LLM models integration from huggingface in monai-deploy-app-sdk. This feature was discussed in #489

The specific model which was integrated in this example is called Prompt2MedImage

Things to do:

1. We need to create an operator for LLM model integration
2. For this particular example, I need to add a JPEG2DICOM converter. For the JPEG2DICOM, we should be able to bring in DICOM metadata from an existing patient data. In absence of such patient data, we should populate the dicom tags with a place holder "John Smith" metadata information.
3. LLMs need specific libraries like transformers and hub (any many more for pre and post processing text data). We need to add these libraries as "optional" requirements for monai-deploy-app-sdk.