Document Dakota as a reference architecture for GNOMEOS and bootc

[castrojo]

https://gitlab.com/freedesktop-sdk/freedesktop-sdk/-/work_items/1975

Dakota · issue pipeline

  ✓  triage     needs kind/ + area/ then /approve
  ▶  discussing —
  ·  queued     —
  ·  claimed    —
  ·  done       —

area: area/upstream   priority: priority/p2
maintainer: reach consensus, then comment /approve
reporter: add spec, context, or requirements to the issue body