Add tagged guidebook versions to enable stable referencing

This is driven from a need to improve the process of filling in 100s of NFRs, particularly for small, single responsibility services.

Example result in draft MR:

root index (includes change to index.md/html): https://uis.uniofcam.dev/-/devops/experiments/ek-599-guidebook/-/jobs/1579441/artifacts/public/index.html

index for tag at /en/0.1.0 https://uis.uniofcam.dev/-/devops/experiments/ek-599-guidebook/-/jobs/1579441/artifacts/public/en/0.1.0/index.html