Add weaviate, pgvector, milvus vector store details

[Nuvindu]

Purpose

Fixes: wso2/product-ballerina-integrator#1077

[pasindufernando1]

@Nuvindu Get the latest changes from main. The fix for the build failure is available now

[MohamedSabthar]

@Nuvindu shall we mark this as draft until we release the vector stores

[Copilot]

Pull Request Overview

This PR adds support for three new vector store implementations (Weaviate, Milvus, and Pgvector) to the flow model generator configuration. Each vector store is configured with appropriate metadata descriptions highlighting their search capabilities and corresponding Ballerina import statements.

• Adds Weaviate vector store with dense and hybrid search support
• Adds Milvus vector store with dense and hybrid search support
• Adds Pgvector vector store with dense, sparse, and hybrid search support

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[NipunaRanasinghe]

@Nuvindu please tag the relevant issue created for this in the PR description

[NipunaRanasinghe]

@MohamedSabthar @Nuvindu are we good to merge this PR? have we released the vector stores as per #243 (comment)?

[nipunayf]

The changes should go to the main branch if we are targeting 1.3.0