Platform: Compile an architecture blueprint for Data Insights Platform

We have been using https://docs.google.com/document/d/1V3XRXfPquBrI_-ob9Fn2Jdskq7W4-heG6zBjJ66AOx8/edit?tab=t.0 as an architecture blueprint so far. It'd be prudent to formally move the contents to https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/ and gather broader feedback across the organisation during the process.