Implement the /models endpoint for the VLLM provider

For some reason, continue in JetBrains needs this otherwise loading the
plugin fails with:
```
Error: HTTP 404 Not Found from http://127.0.0.1:8000/vllm/models

This may mean that you forgot to add '/v1' to the end of your 'apiBase'
in config.json.
    at customFetch (/snapshot/continue/binary/out/index.js:471442:17)
        at process.processTicksAndRejections
        (node:internal/process/task_queues:95:5)
            at async withExponentialBackoff
            (/snapshot/continue/binary/out/index.js:471175:22)
---> continue restarts here
[info] Starting Continue core...
[2024-12-04T08:52:45] [info] Starting Continue core...
```

Author: jhrozek

src/codegate/providers/vllm/provider.py

@@ -1,6 +1,7 @@
 import json
 from typing import Optional
 
+import httpx
 from fastapi import Header, HTTPException, Request
 from litellm import atext_completion
 
@@ -44,6 +45,22 @@ def _setup_routes(self):
         passes it to the completion handler.
         """
 
+        @self.router.get(f"/{self.provider_route_name}/models")
+        async def get_models(authorization: str = Header(..., description="Bearer token")):
+            if not authorization.startswith("Bearer "):
+                raise HTTPException(status_code=401, detail="Invalid authorization header")
+
+            token = authorization.split(" ")[1]
+            config = Config.get_config()
+            base_url = config.provider_urls.get("vllm")
+
+            async with httpx.AsyncClient() as client:
+                response = await client.get(
+                    f"{base_url}/v1/models", headers={"Authorization": f"Bearer {token}"}
+                )
+                response.raise_for_status()
+                return response.json()
+
         @self.router.post(f"/{self.provider_route_name}/chat/completions")
         @self.router.post(f"/{self.provider_route_name}/completions")
         async def create_completion(