Update pinecone backend to use new engines & base class

I have updated the code as required.
Also made some changes in chatbot since namespace was not being passed to the search query when using the chatbot. If required we can handle that as part of a separate issue.

The only concern here is the deletion of items part.
When performing indexing, at first items are deleted from the index. That code was throwing an exception when items were not found in the index. So I added a try catch block.
We need to fix that logic so that we can delete by ID instead of metadata filtering, since deletion by ID is supported for all types of indices in Pinecone.