TOC for the upgrade guide includes old TOC of GHCP

[adegeo]

Describe the issue or suggestion

This TOC needs some adjustments. With how large the GHCP modernization content grew, does it make sense to keep it duplicated in the upgrade guide? I think it should just be a top link in the TOC that navigates to the GHCP overview page and is shown under that normal TOC.

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Associated WorkItem - 576429