[v0.9.1][Doc]Large Scale Ep doc update (#2595)

### What this PR does / why we need it?
Add more details and Optimize the directory structure in the large scale
ep document

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
No

---------

Signed-off-by: hust17yixuan <[email protected]>

Author: hust17yixuan

docs/source/developer_guide/performance/distributed_dp_server_with_large_ep.md

@@ -6,5 +6,4 @@
 performance_benchmark
 profile_execute_duration
 optimization_and_tuning
-distributed_dp_server_with_large_ep
 :::

docs/source/developer_guide/performance/index.md

@@ -9,4 +9,5 @@ multi_npu
 multi_npu_qwen3_moe
 multi_npu_quantization
 multi_node
+large_scale_ep
 :::