qdrant: test new QdrantVectorStore (#24165)
## Description
This PR adds integration tests to follow up on #24164.
By default, the tests use an in-memory instance.
To run the full suite of tests, with both in-memory and Qdrant server:
```
$ docker run -p 6333:6333 qdrant/qdrant
$ make test
$ make integration_test
```
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Co-authored-by: Erick Friis <erick@langchain.dev>
