Add perf-changelog entry placeholder

Record the GPT-OSS MI355X vLLM model update
(amd/gpt-oss-120b-w-mxfp4-a-fp8 -> openai/gpt-oss-120b).

Author: chunfangamd

perf-changelog.yaml

@@ -3474,3 +3474,9 @@
     - "Use scheduler-recv-interval values 2/60/30/1200/600/1920 for conc 1-4/8/16/32/64/128-256"
     - "Set max-running-requests=256, chunked-prefill-size=16384, mem-fraction-static=0.8, cuda-graph-max-bs=CONC, and enable symm-mem"
   pr-link: https://github.com/SemiAnalysisAI/InferenceX/pull/1544
+
+- config-keys:
+    - gptoss-fp4-mi355x-vllm
+  description:
+    - "Update GPT-OSS model for MI355X vLLM from amd/gpt-oss-120b-w-mxfp4-a-fp8 to openai/gpt-oss-120b"
+  pr-link: https://github.com/SemiAnalysisAI/InferenceX/pull/1638