Qdrant - refactor and release a major version

[anakin87]

important

• the embedding_field init parameter of QdrantDocumentStore will break things if not set to the default value ("embedding") -> should be removed
• the return_embedding init parameter of QdrantDocumentStore is not used and is confusing -> should be removed

nice to have

• set the default value for scale_score in Retrievers to False, as we do for all other retrievers
• separate well the tests for Document Store retrieval methods and Retrievers (non breaking)