Improve document stores capabilities: add more operations

[davidsbatista]

Add the following operations to our document stores:

count_documents_by_filter(filter: dict) -> int applies a filter and counts the documents that matched it.

count_distinct_values_by_filter(filter: dict) -> dict[str, int] applies a filter selecting documents and counts the unique values for each meta field of the matched documents

get_fields_info() -> dict[str, dict] returns the meta fields and the corresponding types

get_field_min_max(metadata_field: str) -> dict[str, Any] for a given metadata field, find its max and min value

get_field_unique_values(field_name: 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

query_sql(query: str) - optional - issue an SQL query for the doc stores that support it

[sjrl]

@davidsbatista thanks for making this! Only a few comments on namings

• It seems like our methods in our existing document stores always use the plural filters in their function signature. I think it would make sense to keep that consistent e.g. update count_documents_by_filter(filter: dict) -> int to count_documents_by_filter(filters: dict[str, Any]) -> int
• For the functions get_field_unique_values and get_field_min_max let's decide on a consistent name for the metadata field. I see metadata_field and field_name both being used right now.