Blocking IO call made in AstraDBGraphVectorStore's init

[cbornet]

Even when setup_mode is ASYNC, AstraDBGraphVectorStore spawns a AstraDBVectorStore in SYNC setup_mode:

langchain-datastax/libs/astradb/langchain_astradb/graph_vectorstores.py

Lines 307 to 309 in 25ad55f

	# for the test search, if setup_mode is ASYNC,
	# create a temp store with SYNC
	if setup_mode == SetupMode.ASYNC:

Since the setup mode is SYNC, it makes a blocking HTTP call to create the collection.
So when AstraDBGraphVectorStore is instantiated in an async coroutine, this blocks the event loop.