docs: qdrant in memory usage - #1634

from typing import Optional

from docarray import BaseDoc
from docarray.index import QdrantDocumentIndex
from docarray.typing import NdArray

class MyDocument(BaseDoc):
    title: str
    title_embedding: NdArray[786]
    image_path: Optional[str]
    image_embedding: NdArray[512]


# Creating an in-memory Qdrant document index
qdrant_config = QdrantDocumentIndex.DBConfig(":memory:")
doc_index = QdrantDocumentIndex[MyDocument](qdrant_config)