feat: Add Pinecone online store integration

[SIDDHESH1564]

What this PR does / why we need it:

This PR adds Pinecone as a new online store integration for Feast. Pinecone is a managed vector database that enables fast similarity search and retrieval, making it ideal for ML feature serving workloads that involve embeddings and vector-based lookups.

Key changes:

• Implements PineconeOnlineStore class with full CRUD operations (online_write_batch, online_read, teardown)
• Adds Pinecone as a configurable online store option via PineconeOnlineStoreConfig
• Supports namespace-based isolation for multi-tenant environments
• Handles batch upserts with automatic chunking to respect Pinecone's API limits
• Adds unit tests and integration test configuration

Which issue(s) this PR fixes:

Fixes #6582

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

Misc

• Requires pinecone-client as an optional dependency (pip install feast[pinecone])
• Tested against Pinecone Serverless and Pod-based indexes
• Documentation updated in docs/reference/online-stores/pinecone.md