Expose missing configurations for grpc_config and pool_threads

[jhamon]

Problem

This PR addresses a few configuration-related issues:

• We moved pool_threads configuration up to the Pinecone client instance, but for backwards compatibility it would be nice to also allow it to be passed in the call to pc.Index(host='your-host', pool_threads=5)
• We need to expose grpc_config as a keyword param when targeting indexes via the grpc-flavored client.

Solution

• Pass through kwargs from .Index() to underlying Index class implementation
• Add unit tests making sure pool_threads and grpc_config handled correctly.

Before (pool_threads)

from pinecone import Pinecone

pc = Pinecone(api_key='key', pool_threads=5)
pc.Index(host='host')
pc.upsert(...)

After (pool_threads, add backwards compatibility with old way)

You can use syntax as before, or alternatively can do this:

from pinecone import Pinecone

pc = Pinecone(api_key='key')
index = pc.Index(host='host', pool_threads=5)
index.upsert(...)

After (grpc, allow grpc_config to be passed)

from pinecone.grpc import PineconeGRPC, GRPCClientConfig

pc = PineconeGRPC(api_key='YOUR_API_KEY')
grpc_config = GRPCClientConfig(
    timeout=10, 
    secure=True,
    reuse_channel=True
)
index = pc.Index(name='my-index', host='host', grpc_config=grpc_config)

Type of Change

• New feature (non-breaking change which adds functionality)
• None of the above: Add backwards compatibility on pool_threads config

Test Plan

New tests should be green in CI.

[tdonia]

haven't run it locally but the code + tests make sense!

[austin-denoble]

LGTM 🚢