fix: gpt-3.5-turbo-instruct context size to 8192 (#1196)

api/core/model_providers/models/llm/openai_model.py

     'gpt-4': 8192,
     'gpt-4-32k': 32768,
     'gpt-3.5-turbo': 4096,
-    'gpt-3.5-turbo-instruct': 4096,
+    'gpt-3.5-turbo-instruct': 8192,
     'gpt-3.5-turbo-16k': 16384,
     'text-davinci-003': 4097,
 }

api/core/model_providers/providers/openai_provider.py

             'gpt-4': 8192,
             'gpt-4-32k': 32768,
             'gpt-3.5-turbo': 4096,
-            'gpt-3.5-turbo-instruct': 4096,
+            'gpt-3.5-turbo-instruct': 8192,
             'gpt-3.5-turbo-16k': 16384,
             'text-davinci-003': 4097,
         }