By Elida Moreno and Marianna Parraga PANAMA CITY (Reuters) - The Panama Canal has begun a competitive process to select the company that will design, build and operate a pipeline to transport liquefied petroleum gas (LPG), its authority said on Thursday, following meetings with interested companies. The project, expected to require an investment of between $4 billion and$8 billion, is part of the waterway's move to meet increased demand for services including trans-shipment and generate extra revenue, f ...