Add settings-validation-android.md from Meshtastic-Android PR #5218 (#56)

* Add settings-validation-android.md from Meshtastic-Android PR #5218

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Co-authored-by: garthvh <1795163+garthvh@users.noreply.github.com>

* Move settings-validation-android.md to .github/docs/validation/

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: garthvh <1795163+garthvh@users.noreply.github.com>

Author: Copilot