Add vLLM inference provider for OpenAI compatible vLLM server (#178)

This PR adds vLLM inference provider for OpenAI compatible vLLM server.

llama_stack/providers/adapters/inference/vllm/config.py

@@ -0,0 +1,22 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from typing import Optional
+
+from llama_models.schema_utils import json_schema_type
+from pydantic import BaseModel, Field
+
+
+@json_schema_type
+class VLLMImplConfig(BaseModel):
+    url: Optional[str] = Field(
+        default=None,
+        description="The URL for the vLLM model serving endpoint",
+    )
+    api_token: Optional[str] = Field(
+        default=None,
+        description="The API token",
+    )