[Feature] Add OpenAI embedding model (Java)

[purushah]

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• I searched in the issues and found nothing similar.

Description

Motivation

Python has OpenAIEmbeddingModelConnection and OpenAIEmbeddingModelSetup; Java has only Ollama and Bedrock. A Java agent that needs an OpenAI embedding today must go through the Python wrapper, which requires a Python environment on the task managers for a plain HTTPS call. This is a Java/Python parity gap. The Java OpenAI chat model already depends on com.openai:openai-java, so no new third-party dependency is needed.

Proposed changes

• New module integrations/embedding-models/openai with OpenAIEmbeddingModelConnection and OpenAIEmbeddingModelSetup, built the same way OpenAICompletionsConnection builds its client.
• Arguments mirror the Python classes one for one: connection api_key, base_url, request_timeout, max_retries, organization, project; setup connection, model, encoding_format, dimensions, user, additional_kwargs.
• embedWithUsage reports prompt and total tokens so the embedding token metrics from [api][python][java] Track embedding token usage metrics #870 cover this provider.
• ResourceName constants, YAML aliases, dist registration, and a Java tab in the OpenAI section of embedding_models.md.
• Unit tests with a mocked client, following BedrockEmbeddingModelTest.

One naming question: the Java OpenAI chat connection uses api_base_url and timeout, while the Python embedding connection uses base_url and request_timeout. I propose the Python embedding names so the two embedding implementations align across languages. Happy to follow the chat-model names instead if preferred.

Are you willing to submit a PR?

• I'm willing to submit a PR!

[wenjin272]

Thanks for proposing this. Assigned.