Add support for OpenAI Java SDK (official Java library from OpenAI)

[jdubois]

This follows the discussion on ticket #3368

This is a draft PR as the work is pretty big, I'll start with the simpler implementations (Embeddings) and finish with the more complex one (Chat).

[jdubois]

With today's commit, we now have:

• Support for EmbeddingModel
• Support for ImageModel

And some basic shared configuration, that will be improved next, so we're ready for the more complex stuff (ChatModel).

[jdubois]

The setup logic for the OpenAI SDK should be very similar to this class from LangChain4, because it's basically doing the same thingj:

https://github.com/langchain4j/langchain4j/blob/main/langchain4j-open-ai-official/src/main/java/dev/langchain4j/model/openaiofficial/InternalOpenAiOfficialHelper.java

I'm very careful before taking code from another project, but I believe this is fine: I'm the author of that other class, so I have the copyright on this code. Also, it's simple logic to connect to Azure/GitHub Models/OpenAI, nothing that is very specific or critical.

However, if this causes problems:

• I can talk to OpenAI to check if that can be included into their code (I don't think they'll agree as they try to have something generic)
• I can create my own library, but having both projects depend on a small library that I would maintain doesn't seem a good idea to me

Happy to discuss this if needed.

[jdubois]

Argh, I updated my fork and now my commit history is all wrong!!!! I'll do my best to fix this.

[jdubois]

I had to force push my fork, sorry if anyone had this pulled on their side! I'll check if everything is good, otherwise I have a backup on my laptop.