[Feature] Warn about unrecognized environment variables (#33581)

Signed-off-by: Gregory Shtrasberg <Gregory.Shtrasberg@amd.com>

vllm/envs.py

@@ -1606,6 +1606,15 @@ def is_set(name: str):
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
 
 
+def validate_environ(hard_fail: bool) -> None:
+    for env in os.environ:
+        if env.startswith("VLLM_") and env not in environment_variables:
+            if hard_fail:
+                raise ValueError(f"Unknown vLLM environment variable detected: {env}")
+            else:
+                logger.warning("Unknown vLLM environment variable detected: %s", env)
+
+
 def compile_factors() -> dict[str, object]:
     """Return env vars used for torch.compile cache keys.