fix: replace Completion with ChatCompletion to use `gpt-3.5-turbo…

…` model (#2066)

According to https://platform.openai.com/docs/guides/gpt/chat-completions-vs-completions , GPT-3.5 Turbo & GPT-4 is not working on **Legacy** Completions API

apiserver/plane/api/views/gpt.py

@@ -41,17 +41,17 @@ def post(self, request, slug, project_id):
             final_text = task + "\n" + prompt
 
             openai.api_key = settings.OPENAI_API_KEY
-            response = openai.Completion.create(
+            response = openai.ChatCompletion.create(
                 model=settings.GPT_ENGINE,
-                prompt=final_text,
+                messages=[{"role": "user", "content": final_text}],
                 temperature=0.7,
                 max_tokens=1024,
             )
 
             workspace = Workspace.objects.get(slug=slug)
             project = Project.objects.get(pk=project_id)
 
-            text = response.choices[0].text.strip()
+            text = response.choices[0].message.content.strip()
             text_html = text.replace("\n", "<br/>")
             return Response(
                 {