Ensure ModelInfo field is serialized for OpenAIChatCompletionClient (#5315)

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## Why are these changes needed?

Fix bug where the `model_info` field is not serialized for the
`OpenAIChatCompletionClient` class. This was because the `_raw_config`
field was based on a version of the args that had been sanitized
(model_info removed). We need the full model info field for non-openai
models

```python
from autogen_ext.agents.web_surfer import MultimodalWebSurfer
from autogen_ext.models.openai import OpenAIChatCompletionClient
from autogen_core.models import ModelInfo
mistral_vllm_model = OpenAIChatCompletionClient(
    model="TheBloke/Mistral-7B-Instruct-v0.2-GGUF",
    base_url="http://localhost:1234/v1",
    api_key="empty",
    model_info=ModelInfo(vision=False, function_calling=True, json_output=False, family="unkown"),
)
(mistral_vllm_model.dump_component().model_dump_json())
```

Before
```
{
  "provider": "autogen_ext.models.openai.OpenAIChatCompletionClient",
  "component_type": "model",
  "version": 1,
  "component_version": 1,
  "description": "Chat completion client for OpenAI hosted models.",
  "label": "OpenAIChatCompletionClient",
  "config": {
    "model": "TheBloke/Mistral-7B-Instruct-v0.2-GGUF",
    "api_key": "empty",
    "base_url": "http://localhost:1234/v1"
  }
}

```

After
```
{
  "provider": "autogen_ext.models.openai.OpenAIChatCompletionClient",
  "component_type": "model",
  "version": 1,
  "component_version": 1,
  "description": "Chat completion client for OpenAI hosted models.",
  "label": "OpenAIChatCompletionClient",
  "config": {
    "model": "TheBloke/Mistral-7B-Instruct-v0.2-GGUF",
    "api_key": "empty",
    "model_info": {
      "vision": false,
      "function_calling": true,
      "json_output": false,
      "family": "unkown"
    },
    "base_url": "http://localhost:1234/v1"
  }
}


```
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solves. -->

## Related issue number

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introduced in this PR.
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python/packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py

@@ -1062,7 +1062,9 @@ class OpenAIChatCompletionClient(BaseOpenAIChatCompletionClient, Component[OpenA
             raise ValueError("model is required for OpenAIChatCompletionClient")
 
         model_capabilities: Optional[ModelCapabilities] = None  # type: ignore
+        self._raw_config: Dict[str, Any] = dict(kwargs).copy()
         copied_args = dict(kwargs).copy()
+
         if "model_capabilities" in kwargs:
             model_capabilities = kwargs["model_capabilities"]
             del copied_args["model_capabilities"]
@@ -1074,7 +1076,7 @@ class OpenAIChatCompletionClient(BaseOpenAIChatCompletionClient, Component[OpenA
 
         client = _openai_client_from_config(copied_args)
         create_args = _create_args_from_config(copied_args)
-        self._raw_config: Dict[str, Any] = copied_args
+
         super().__init__(
             client=client, create_args=create_args, model_capabilities=model_capabilities, model_info=model_info
         )