Support LIKE/contains filtering for string attributes

[dfalbel]

Summary

The attribute filter layer currently supports eq, ne, gt, gte, lt, lte, in, and nin operators. There's no way to do substring/pattern matching on string attributes.

Motivation

When attributes store comma-separated values (e.g. labels = "bug, enhancement"), exact equality filters like labels = 'bug' won't match. A LIKE operator would allow patterns like labels LIKE '%bug%' to find partial matches.

This came up in the GitHub issues RAG example, where issue labels are stored as a comma-separated string and users want to filter by a single label.

Backend support

• DuckDB: Native LIKE support
• ChromaDB: Has $contains operator (equivalent)
• OpenAI: Unsupported (raise an error)