Bump assistant plugin (#534)

# Update Pinecone Assistant Plugin to v3.0.0

## Summary

This PR updates the `pinecone-plugin-assistant` dependency from `^1.6.0`
to `3.0.0`.

## Changes

- Updated `pinecone-plugin-assistant` version constraint in
`pyproject.toml` from `^1.6.0` to `3.0.0`
- Updated `poetry.lock` to reflect the new dependency version and
resolved sub-dependencies

## Breaking Changes

None - This is a dependency version update only.

Author: jhamon