[Feature:RainbowGrades] Integration testing

[dagemcn]

Why is this Change Important & Necessary?

Closes Issue#10436.

What is the New Behavior?

Adds integration testing for the behavior of extra credit in rainbow grades.

What steps should a reviewer take to reproduce or test the bug or new feature?

Check out this branch, read through the readme.md in the integrationTests folder and the readme.md in tests/extra_credit

1. Run the tests run and pass locally from the integration tests folder with ./run.py.
2. Run a single test module using ./run.py <module name here>
3. Run a single testcase within a module using ./run.py extra_credit.all_students_summary_csv
4. Make a change to how extra credit is calculated and run the tests again to observe the failures

• Test updating the golden files (baseline examples to compare to) using ./run.py --update and run the tests again, observe the tests pass

Automated Testing & Documentation

Testing added in this PR

Other information

This is not a breaking change, no security concerns with this PR.