Plugin lazy loading

[jhamon]

Problem

We want to ensure that plugins do not add latency to the client initialization process. We don't want to load plugins unless the user is attempting to use them.

This will soon become important because we want to take a dependency on the knowledge plugin that is only used by a fraction of our total users.

Solution

• Refactor the PluginAware class to implement lazy loading with __getattr__. In this way, we avoid spending time and memory loading in plugins that may be present but unused.
• Adjust usage of PluginAware in Pinecone, Index, and Inference classes.

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

Describe specific steps for validating this change.