[FEA]: Add bm25 to supported indexes in vdb task (milvus)

[jperez999]

Is this a new feature, an improvement, or a change to existing functionality?

New Feature

How would you describe the priority of this feature request

Significant improvement

Please provide a clear description of problem this feature solves

This PR will add bm25 support provided by Milvus to the VDBTask sink. This will unlock hybrid search where we can query against both BM25 and model embeddings.

Describe the feature, and optionally a solution or implementation and any alternatives

We would allow the user to activate this feature using a boolean when they create the vdb task for their pipeline.
i.e.
VDBTask(bm25=True), This will load both the model embedding index and a bm25 index.

Additional context

No response