Use max_completion_tokens for OpenAI

Keep the existing maxTokens configuration key for backward compatibility while sending OpenAI-compatible chat completion payloads with max_completion_tokens.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Kai Kreuzer <kai@openhab.org>

Author: kaikreuzer

bundles/org.openhab.binding.chatgpt/src/main/java/org/openhab/binding/chatgpt/internal/api/dto/ChatRequestBody.java

@@ -28,7 +28,7 @@ public class ChatRequestBody {
     private Double temperature;
     @JsonProperty("top_p")
     private Double topP;
-    @JsonProperty("max_tokens")
+    @JsonProperty("max_completion_tokens")
     private Integer maxTokens;
     private String user;
     private List<ChatTools> tools;