docs: add integration documentation for pegatron RU

Ravi Shankar Prasadrequested to merge
ontherays/ocudu_docs:feature/add-new-ru-docs into main

This merge request adds a new integration guide (`pegatron.md`) to the OCUDU documentation, detailing the setup and configuration required for Pegatron 5G O-RAN Radio Units (specifically the PR1450-78I model).

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