[Misc] Add generated git commit hash as vllm.__commit__ (#6386)

tests/test_embedded_commit.py

@@ -0,0 +1,7 @@
+import vllm
+
+
+def test_embedded_commit_defined():
+    assert vllm.__commit__ != "COMMIT_HASH_PLACEHOLDER"
+    # 7 characters is the length of a short commit hash
+    assert len(vllm.__commit__) >= 7