modified retrievers to support optional node labels

[gurveervirk]

Description

Note

Adds support for optional node label filtering to the external retrievers: WeaviateNeo4jRetriever, QdrantNeo4jRetriever, and PineconeNeo4jRetriever.

• Introduces an optional node_label parameter to the retriever constructors and models.
• Updates Cypher query generation to use the label in the MATCH clause if provided.
• Passes node_label from the retriever to the query logic.
• Addresses issue #344.

Type of Change

• [x] New feature
• [ ] Bug fix
• [ ] Breaking change
• [ ] Documentation update
• [ ] Project configuration change

Complexity

Note

Please provide an estimated complexity of this PR of either Low, Medium or High

Complexity: Medium

How Has This Been Tested?

• [ ] Unit tests
• [ ] E2E tests
• [x] Manual tests

Checklist

The following requirements should have been met (depending on the changes in the branch):

• [ ] Documentation has been updated
• [ ] Unit tests have been updated
• [ ] E2E tests have been updated
• [ ] Examples have been updated
• [ ] New files have copyright header
• [ ] CLA (https://neo4j.com/developer/cla/) has been signed
• [ ] CHANGELOG.md updated if appropriate