OpenAI - improve error messages when there is a connection error

Expected Behavior

It would be great to have an explicit error message when the connection with OpenAI cannot be established.

Current Behavior
(Using Spring AI 0.8.1)
Messages are quite hard to understand when there is a connection error with the OpenAI API.
For instance, if there is a mistake in my API key, I get the following error:

2024-05-26T21:23:44.729+08:00  WARN 43707 --- [petclinic-prompt] [           main] o.s.a.a.r.SpringAiRetryAutoConfiguration : Retry error. Retry count:1

org.springframework.web.client.RestClientException: Error while extracting response for type [org.springframework.ai.openai.api.OpenAiApi$ChatCompletion] and content type [application/json;charset=utf-8]
	at org.springframework.web.client.DefaultRestClient.readWithMessageConverters(DefaultRestClient.java:240) ~[spring-web-6.1.8.jar:6.1.8]
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.readBody(DefaultRestClient.java:688) ~[spring-web-6.1.8.jar:6.1.8]

Using curl, we are getting an error message that is easier to understand, so I thought it might be possible to improve it in Spring AI:

Calling OpenAI
{
    "error": {
        "message": "Incorrect API key provided: sk-proj-*********************************************F2yw. You can find your API key at https://platform.openai.com/account/api-keys.",
        "type": "invalid_request_error",
        "param": null,
        "code": "invalid_api_key"
    }
}

Thanks a lot for the great work!

Start by tracing the OpenAI request from OpenAiApi$ChatCompletion through Spring's RestClient and the SpringAiRetryAutoConfiguration warning shown in the report. Reproduce the invalid API-key response and determine where the response is converted into the generic RestClientException. Done means connection and authentication failures expose a clear, actionable message like the API error shown by curl.