fix #2038 Add custom-headers to the Azure Open AI Spring Boot Starter

[arey]

Fix issue langchain4j/langchain4j#2038

Is there any markdown documentation file to complete?
Do I need to create an integration test? If so, how?

[langchain4j]

@arey thank you!
Could you please add thease headers for other model types as well (e.g. embedding, etc)?
I am not sure how to automate testing this. Perharps you could test it manually?

[arey]

I've also added the customHeaders property to the EmbeddingModelProperties and ImageModelProperties class.
I've tested the change manually from my laptop.
In the logs of the azure client, we can see that the custom-header header has been append to the redactedHeaders as expected:

2024-11-07T08:10:25.790+01:00 INFO 97681 --- [nio-8080-exec-2] c.a.a.o.i.O.getChatCompletionsSync : {"az.sdk.message":"HTTP request","method":"POST","url":"https://xxxx.azure-api.net/openai/deployments/gpt-4o/chat/completions?api-version=2024-07-01-preview","tryCount":1,"Date":"Thu, 07 Nov 2024 11:10:25 GMT","Content-Type":"application/json","x-ms-client-request-id":"ca47656d-099f-4f9c-8137-3bd8a9905ad9","Accept":"application/json","User-Agent":"langchain4j-azure-openai","redactedHeaders":"api-key,custom-header","content-length":16516}

[langchain4j]

@arey thanks a lot!