adding VDMS retriever and test - The VDMS retriever and test are implemented in this PR. PLEASE NOTE: The input for retriever is EmbedDoc and return is SearchedDoc (these types may need to be updated for service integration)

adding VDMS retriever and test - The VDMS retriever and test are implemented in this PR. PLEASE NOTE: The input for retriever is EmbedDoc and return is SearchedDoc (these types may need to be updated for service integration) #69