add the following operations to `QdrantDocumentStore`

[davidsbatista]

def count_documents_by_filter(filter: dict) -> int

• applies a filter and counts the documents that matched it.

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def count_unique_metadata_by_filter(filters: dict[str, Any], metadata_fields: list[str]) -> dict[str, int]` 

• applies a filter selecting documents and counts the unique values for each meta field of the matched documents

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def get_metadata_fields_info() -> dict[str, dict]

• returns the meta fields and the corresponding types, it should return the same format as in the OpenSearchDocumentStore

{
    'content': {'type': 'text'},
    'category': {'type': 'keyword'},
    'status': {'type': 'keyword'},
    'priority': {'type': 'long'},
}

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def get_metadata_field_min_max(metadata_field: str) -> dict[str, Any]

• for a given metadata field, find its max and min value

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def get_metadata_field_unique_values(metadata_field: str, search_term: str | None, from_: int, size: int) -> tuple[list[str], int]:

• retrieves unique values for a field matching a search_term or all possible values if no search term is given

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def query_sql(query: str)

• (optional) issue an SQL query for the doc stores that support it