Add qdrant CLI support and fix support for optional fields

[s-h-a-d-o-w]

While working on CLI support using qdrant's docker image, I came across the problem that the current implementation to support empty strings actually doesn't seem to work. Using an empty string resulted in the following error:

  File "C:\Users\andy\temp\VectorDBBench\vectordb_bench\backend\clients\qdrant_cloud\cli.py", line 39, in QdrantCloud
    db_config=QdrantConfig(**config_params),
              ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "pydantic\\main.py", line 347, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 1 validation error for QdrantConfig
api_key
  none is not an allowed value (type=type_error.none.not_allowed)

I guess pydantic interprets empty strings as None?
To resolve this, I made this field actually optional (instead of relying on empty string) and added handling for optional fields to the frontend.

If you like these changes, what do you think about renaming things to just "qdrant" (no "cloud") and making http://localhost:6333 the default value for url?

[sre-ci-robot]

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This pull-request has been approved by: alwayslove2013, s-h-a-d-o-w
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