OpenAI dependency

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Hello, I am facing this issue:
` File "/app/app/src/router/__init__.py", line 5, in
from .gateway.router import router as gateway_router
File "/app/app/src/router/gateway/router.py", line 4, in
from routellm.controller import Controller
File "/usr/local/lib/python3.12/site-packages/routellm/controller.py", line 10, in
from routellm.routers.routers import ROUTER_CLS
File "/usr/local/lib/python3.12/site-packages/routellm/routers/routers.py", line 17, in
from routellm.routers.matrix_factorization.model import MODEL_IDS, MFModel
File "/usr/local/lib/python3.12/site-packages/routellm/routers/matrix_factorization/model.py", line 4, in
from routellm.routers.similarity_weighted.utils import OPENAI_CLIENT
File "/usr/local/lib/python3.12/site-packages/routellm/routers/similarity_weighted/utils.py", line 11, in
OPENAI_CLIENT = OpenAI()
^^^^^^^^
File "/usr/local/lib/python3.12/site-packages/openai/_client.py", line 104, in __init__
raise OpenAIError(
openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY environment variable`
Of course, I can set the environment variable, but I don't want to depend on it. It would be preferable to have a way to set the base_url, model, and api_key for this client as well.

Start at app/src/router/gateway/router.py and follow the RouteLLM Controller import shown in the traceback. Trace where the OpenAI client is initialized and determine how configuration could reach it without requiring OPENAI_API_KEY. Done should allow the base URL, model, and API key to be supplied through the application rather than only the environment.

Written by the indexing model from the issue text.