Add technical writers to product/stage pages

Why is this change being made?

I noticed that the updated TW assignments weren't reflecting properly in:

• https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
• https://about.gitlab.com/handbook/product/categories/

This updates the data for Marcin, Nick and Mike J, while also preparing for Amy and Suzanne to take over their own stages next release.

Verified both pages in the Review App and both are fixed by this MR.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what