Split Certify group from Product Planning

Why is this change being made?

As part of the approved changes in Product#1698 (closed):

Knowledge PM Christen Dybenko will transition to the Portfolio Management PM role and we will undo the merger of Portfolio Management and Certify. Mark Wood will continue to own the three Certify categories, but will transition to primarily serve as the Gitaly PM. This aligns well with PM skill set and subject matter expertise. Requirements Management is a seedling we should continue to nurture and is best run by Mark Wood.

This MR revitalizes the Certify group as part of #9596 (closed). We will retain the group name Product Planning.

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