Add 10 generator system to phasor dynamics examples

[pelesh]

Description

Add a phasor dynamics example to simulates a 11-bus system with 10 Genrou 6th order generator models split in two groups of five generators. The two groups are connected by a high-impedance branch, which makes connection between them weak.

@Steven-Roberts

Proposed changes

This could be a helpful use case for testing multi method numerical integration schemes. The example outputs generator speeds and voltage magnitudes on electrical buses. The example is documented with minimalistic code comments.

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• N/A There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.

Further comments

[abdourahmanbarry]

This looks good!