Update migrate_to_pinecone.py

[ericx00]

Pinecone Initialization:

Uses pinecone.init() and checks if the specified index exists.
Adds an environment variable for the Pinecone environment (e.g., us-west1-gcp).

Metadata Preservation:

Includes all metadata from ChromaDB in the migration process and appends the document text to the metadata.

Batching Robustness:

Handles cases where the dataset is not evenly divisible by the batch size.

Error Handling:

Validates data consistency and raises errors for missing index or improper configurations.

Progress Feedback:

Adds a progress bar using tqdm for better user experience.