Update links to public docs

What does this MR do and why?

Previous links to Unit Primitive context was gated behind confidential issue links. This MR updates the link to publicly available documentation.

This was identified by @abitrolly in gitlab-org/modelops/applied-ml/code-suggestions/ai-assist#512 (comment 1953971642).

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.