feat: add HybridVectorStore API

[mhordynski]

Feature description

The class accepts a dictionary containing VectorStore objects that are to be used underneath. By default, when writing to all vector stores, all passed elements are saved, but there should be the option to customize this behavior—"routing" which element goes to which store or modifying elements based on the store. This could likely take the form of a function/method that takes in the entire list of elements and the name (?) of the vector store, and returns a list of elements that should go to that store. By default, all elements are returned, but they can also be filtered, for example, saving a certain aspect of an element in one store (e.g., text) and another aspect in another store (e.g., image).

When querying, there should optionally be the capability to choose which stores we want to search through. If the same element is returned by multiple stores (the class must be able to detect this), the results should be automatically deduplicated. There should be configurable strategies for how this affects the order of elements (you could model this on, for example, strategies used in Qdrant).

Motivation

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Additional context

No response