VectorStore filter improve

[YoKv]

in my case, i use milvus and want to use json_contains_any

Proposal: Make ExpressionType an Interface for Extensibility

Problem

The current implementation of ExpressionType in Filter.java is an enum with fixed operation types (AND, OR, EQ, NE, etc.). This limits the ability of vector store implementations to support custom operation types that might be specific to their underlying storage systems.

Current Implementation

public enum ExpressionType {
    AND, OR, EQ, NE, GT, GTE, LT, LTE, IN, NIN, NOT
}

Proposed Solution

Convert ExpressionType from an enum to an interface, allowing different vector store implementations to define their own operation types. This would make the filter system more flexible and extensible.