Remove query generator defualt topk

[acatav]

Problem

We currently have two default top k and it's confusing

Solution

Remove default top k from query generator, and make it to pass None in top_k so KB will use its default. We still support passing top_k in queries to context engine, but it also possible to not pass and top_k to use the KB default

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Unit tests adjusted

[igiloh-pinecone]

@acatav Approved, but please see one comment