Standardize the usage of pyomo.environ imports

[mrmundt]

Fixes NA

Summary/Motivation:

Inspired by #1026, this standardizes across all documentation and code to use import pyomo.environ as pyo rather than as pe.

Changes proposed in this PR:

• Replace import pyomo.environ as pe with import pyomo.environ as pyo

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[jsiirola]

You might also want to grep for typyo's in case I missed one...