Updated to LangChain4j 0.29.0

[langchain4j]

Hi @marcushellberg!
Do you mind if I update the code to use the latest (0.29.0) LangChain4j version and its latest features?

Changes in this PR:

• Using langchain4j-open-ai-spring-boot-starter auto-configuration instead of manually creating OpenAiStreamingChatModel
• Using declarative AI Service instead of manually creating LangChain4jAssistant
• Removed manual creation of OpenAiTokenizer as it is now automatically provided by langchain4j-open-ai-spring-boot-starter
• Changed the tokenizer configuration to split into segments of 50 tokens, because the current setting (200) does not split, as the terms-of-service.txt is only 162 tokens long
• Removed unnecessary ollama and mapdb dependencies

Please let me know if you want me to do any other adjustments.
Thank you!

[marcushellberg]

Looks good. Thanks a lot for contributing!

[langchain4j]

Great, thank you!