Docs: Deprecate maxTokens in favor of maxCompletionTokens for OpenAI chat options

 - Add new option 'maxCompletionTokens' to spring.ai.openai.chat.options
 - Mark 'maxTokens' as deprecated
 - Update documentation to reflect these changes in OpenAI chat configuration

 Related to #1411 and #1412

Author: tzolov

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/chat/openai-chat.adoc

@@ -99,7 +99,8 @@ The prefix `spring.ai.openai.chat` is the property prefix that lets you configur
 | spring.ai.openai.chat.options.temperature | The sampling temperature to use that controls the apparent creativity of generated completions. Higher values will make output more random while lower values will make results more focused and deterministic. It is not recommended to modify `temperature` and `top_p` for the same completions request as the interaction of these two settings is difficult to predict. | 0.8
 | spring.ai.openai.chat.options.frequencyPenalty | Number between -2.0 and 2.0. Positive values penalize new tokens based on their existing frequency in the text so far, decreasing the model's likelihood to repeat the same line verbatim. | 0.0f
 | spring.ai.openai.chat.options.logitBias | Modify the likelihood of specified tokens appearing in the completion. | -
-| spring.ai.openai.chat.options.maxTokens | The maximum number of tokens to generate in the chat completion. The total length of input tokens and generated tokens is limited by the model's context length. | -
+| spring.ai.openai.chat.options.maxTokens | (Deprecated in favour of `maxCompletionTokens`) The maximum number of tokens to generate in the chat completion. The total length of input tokens and generated tokens is limited by the model's context length. | -
+| spring.ai.openai.chat.options.maxCompletionTokens | An upper bound for the number of tokens that can be generated for a completion, including visible output tokens and reasoning tokens. | -
 | spring.ai.openai.chat.options.n | How many chat completion choices to generate for each input message. Note that you will be charged based on the number of generated tokens across all of the choices. Keep `n` as 1 to minimize costs. | 1
 | spring.ai.openai.chat.options.presencePenalty | Number between -2.0 and 2.0. Positive values penalize new tokens based on whether they appear in the text so far, increasing the model's likelihood to talk about new topics. | -
 | spring.ai.openai.chat.options.responseFormat.type | Compatible with `GPT-4o`, `GPT-4o mini`, `GPT-4 Turbo` and all `GPT-3.5 Turbo` models newer than `gpt-3.5-turbo-1106`. The `JSON_OBJECT` type enables JSON mode, which guarantees the message the model generates is valid JSON.