[Onboarding] Fly doc

[github-actions]

Documentation to Add to Onboarding

PR: Fly doc (#2143)
Author: @revmag
PR Link: #2143

Documentation Files Changed:

• ➕ data/docs/metrics-management/fly-metrics.mdx

Context:

This issue was auto‑generated because the PR carries the add-to-onboarding label. Please include these docs into the onboarding flow during the next sprint.