Allow non-admins to use OpenAI routes

The problem we were having is non-admin users trying to use
`/engines/{model}/chat/completions` were getting an HTTP 401 error.

```shell
$ curl -sSL 'http://localhost:4000/engines/gpt-35-turbo-0125/chat/completions' \
    --header "Authorization: Bearer ${LITELLM_KEY}" \
    --header 'Content-Type: application/json' \
    --data ' {
        "model": "gpt-35-turbo-0125",
        "messages": [
            {
                "role": "user",
                "content": "Write a poem about LiteLLM"
            }
        ]
    }' \
    | jq '.'
{
  "error": {
    "message": "Authentication Error, Only proxy admin can be used to generate, delete, update info for new keys/users/teams. Route=/engines/gpt-35-turbo-0125/chat/completions. Your role=unknown. Your user_id=someone@company.com",
    "type": "auth_error",
    "param": "None",
    "code": 401
  }
}
```

This seems to be related to code in `user_api_key_auth` that checks that the URL
matches a list of routes that are allowed for non-admin users, where the list of
routes is in `LiteLLMRoutes.openai_routes.value`. The problem is that the route
`/engines/{model}/chat/completions` is not in that list and furthermore, that
wouldn't even work if it were, because the comparison is done with
`request.url.path` and that will have the actual model name in it (e.g.:
`gpt-35-turbo-0125`), rather than `{model}`.

I added a new list `LiteLLMRoutes.openai_route_names` and added the route
**names** to that list. Then I added a check in `user_api_key_auth` to see if
the route name is in the list of route names.

litellm/proxy/_types.py

@@ -77,6 +77,16 @@ class LiteLLM_UpperboundKeyGenerateParams(LiteLLMBase):
 
 
 class LiteLLMRoutes(enum.Enum):
+    openai_route_names: List = [
+        "chat_completion",
+        "completion",
+        "embeddings",
+        "image_generation",
+        "audio_transcriptions",
+        "moderations",
+        "model_info_v1",
+        "model_info_v2",
+    ]
     openai_routes: List = [
         # chat completions
         "/openai/deployments/{model}/chat/completions",

litellm/proxy/proxy_server.py

@@ -1073,6 +1073,8 @@ async def user_api_key_auth(
             if not _is_user_proxy_admin(user_id_information):  # if non-admin
                 if route in LiteLLMRoutes.openai_routes.value:
                     pass
+                elif request['route'].name in LiteLLMRoutes.openai_route_names.value:
+                    pass
                 elif (
                     route in LiteLLMRoutes.info_routes.value
                 ):  # check if user allowed to call an info route