[Fix] Rename Index class to fix plugin installation

[jhamon]

Problem

By renaming the Index class to _Index in #418, I accidentally broke plugin installation.

Solution

Rename the class back to Index and instead alias it to _Index through import statements. We still need to alias it within the pinecone/data/__init__.py module definition to avoid collision with the Index class designed to give users a more informative error when they incorrectly import the Index class from the pinecone module.

I went ahead and also cleaned up some stuff where we were unnecessarily exposing some internal openapi details in the public interface. Users should never realistically need to construct openapi request objects.

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)

[jseldess]

LGTM, though I'm not really qualified to say so :)

[austin-denoble]

Nice thinking getting these out of here. 👍