docs: update dia spec to v0.6.0
Created by: ashleythedeveloper
This PR updates the DIA specification page to align with the v0.6.0 data model.
NOTE: The external example DIA (link, QR code) will be updated at a later date.
The changes include:
- Update external inks to point to v0.6.0 artefacts (DIA and UNTP Core)
- Update the image of the data model
- Update JSON examples to align with v0.6.0
- Tweaks to the descriptions
- Adding the missing DIA link to Architecture.md