feat: Add Dragonfly vector database cookbook with hybrid search examples

[vyavdoshenko]

Summary

This PR introduces a comprehensive Dragonfly vector database cookbook with practical examples of vector similarity search and hybrid queries using OpenAI embeddings, plus improvements to the Redis examples.

Motivation

This addition makes Dragonfly accessible to OpenAI Cookbook users and provides a practical alternative to Redis for vector database use cases, while also improving the Redis examples with proper dependency management.

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[vyavdoshenko]

Nobody even looked at this PR. If maintainers don't want to receive changes, mention it in the README. If there's something wrong with this PR, please don't hesitate to point it out. If this PR is not desired to be merged, tell me here.