Add support for deleting vectors from pinecone on deletion of document

[siddnikh]

• This PR adds a function that deletes vectors from pinecone database on deletion of document (by superuser or admin)

Since each document has it's own namespace, we can delete the whole namespace on deletion of the document.

[shivankacker]

@siddnikh can you club this with #64 ? Both of these fall hand in hand. We have to delete only certain vectors from a namespace if a Document gets deleted, which can only happen if it contains the relevant meta data