Refactor Microgrid Examples to Facilitate Code Reuse

[abdourahmanbarry]

Description

In this pull request, we separated the construction of the microgrid network from the examples to improve code reuse.

This is the first of four stacked pull requests that split PR #492 into smaller, more manageable chunks.

Proposed changes

Two functions, buildScaleMicrogridNetwork and assembleSystem, were introduced to build the microgrid network and add the components of the network to SystemPowerElectronicsModel, respectively. These functions are then used to replace the network construction and the system model assembly code in all examples. This helps facilitate code reuse as more examples rely on this model.

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• The CHANGELOG.md has been updated to reflect the changes. If this is a minor PR that is part of a larger fix already included in the file, state so.