RDK-61247: Updated the documentation

[tukken-comcast]

Reason for change: Updated the documentation
Test Procedure: Verify docs/NetworkManagerPlugin.md reflects content in definition/NetworkManager.json
Priority: P1
Risk: Low

[Copilot]

Pull request overview

Updates the NetworkManager plugin Markdown documentation to better align with the JSON-RPC API definition, specifically around the GetIPSettings result fields.

Changes:

• Corrects the ula field description from “Unified” to “Unique” local address.
• Updates the GetIPSettings example response ula value.

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