Add Support for AzureOpenAI based64 format embedding responses

[wpanas]

Expected Behavior
It is possible to set encodingFormat in AzureOpenAiEmbeddingOptions the same way as it's possible for OpenAiEmbeddingOptions.

Current Behavior
The default encodingFormat is used which is inefficient for high-load traffic. For companies that aren't using OpenAI embedding models directly it's impossible to change it in Spring AI.

Context
There was a change implemented in #3786 for OpenAI integration, but it has to be mirrored to be available for AzureOpenAI. Without it we can't benefit for improved performance of base64 encoded embeddings. We can workaround it by using Azure SDK for Java without Spring AI, but we loose all the good features the project gives us.

[sunyuhan1998]

Hi @wpanas ! Thank you for your feedback! Previously, I submitted a PR to OpenAiApi to support encodingFormat=base64 (#3804), so I thought I could mirror this capability to AzureOpenAI. However, I noticed that com.azure.ai.openai.models.EmbeddingsOptions#setEncodingFormat is not a public method, which prevents us from setting this option. This seems like a bug to me—what do you think?

[wpanas]

Hi @sunyuhan1998, thanks for swift reply. You might be right. I'll open an issue in Azure SDK for Java and link it with this one

[sunyuhan1998]

Hi @sunyuhan1998, thanks for swift reply. You might be right. I'll open an issue in Azure SDK for Java and link it with this one

Ah! We had the same idea—I've already submitted an issue and a PR. Perhaps we can follow up together here: Azure/azure-sdk-for-java#46531

[wpanas]

It seems that this issue can be resolved only after #4680