Improve pinecone hybrid search retriever adding metadata support

[lbsnrs]

Improve pinecone hybrid search retriever adding metadata support

I simply remove the hardwiring of metadata to the existing implementation allowing one to pass metadatas attribute to the constructors and in get_relevant_documents. I also add one missing pip install to the accompanying notebook (I am not adding dependencies, they were pre-existing).

First contribution, just hoping to help, feel free to critique :)
my twitter username is @andreliebschner

While looking at hybrid search I noticed #3043 and #1743. I think the former can be closed as following the example right now (even prior to my improvements) works just fine, the latter I think can be also closed safely, maybe pointing out the relevant classes and example. Should I reply those issues mentioning someone?

@dev2049, @hwchase17

[dev2049]

thanks @lbsnrs! looks good to me