Update acpt.md to fix docs sidebar (#20927)

ACPT docs should be nested inside Ecosystem category in the docs
sidebar, but they currently show up outside of the category at the top
of the sidebar.

Need to add parent to address this issue.

### Description
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### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
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docs/ecosystem/acpt.md

@@ -1,6 +1,7 @@
 ---
 title: Azure Container for PyTorch (ACPT)
 description: Learn more about Azure Container for PyTorch (ACPT) and how it utilizes ONNX Runtime
+parent: Ecosystem
 nav_order: 1
 redirect_from: /docs/tutorials/ecosystem/acpt
 ---