docs: update 3-1-roles-permissions-overview.md

[habib424]

Drafted by Ship Ship 🚢 — confidence 🟢 high

What changed

Added a note that the SaaS Metrics dashboard is restricted to Admin users only, following the recent permission change that moved this feature from all roles to Admin-only access.

Source PRs

• axolotl#4378 — chore/BLUE-1036/saas-metrics-permissions

How to use this PR

1. Review the diff against the existing article — focus on accuracy and customer voice.
2. Merge if it reads well. Edit and push to this branch if it needs adjustment.
3. Close without merging if the article doesn't actually need this update.

Once we have a track record of clean drafts, we'll graduate to auto-merge with a delay buffer. For now: human-in-the-loop.