feat(notebooks): port vectorizers notebook from Python to Java

Ported from: /Users/brian.sam-bodden/Code/redis/py/redis-vl-python/docs/user_guide/04_vectorizers.ipynb

Maintains fidelity to Python examples with Java adaptations:
- Same test sentences and models
- OpenAI vectorizer (text-embedding-ada-002)
- HuggingFace Sentence Transformers (all-mpnet-base-v2)
- Cohere vectorizer (embed-english-v3.0)
- VoyageAI vectorizer (voyage-law-2)
- LangChain4j integration example (Azure OpenAI)
- Custom vectorizer implementation
- Vector search example with same data
- Data type selection (FLOAT16, FLOAT32, FLOAT64)

Minimal markdown adjustments to reflect Java API usage while preserving original content structure and teaching flow.

Author: bsbodden