Run AEP Apex Sample Code tests against the core AEP Commons library on each push

[daveespo]

Is your feature request related to a problem? Please describe.

There are certain code paths that can't be exercised with test coverage in this repository. Notably, Field Sets can't be covered because no standard SObject exists that has a field set.

Describe the solution you'd like

We should be able to a deploy the fflib-apex-common-samplecode project into the scratch org that's being used to run the unit tests and have all tests run (the same way we deploy fflib-apex-mocks into the scratch org)

Describe alternatives you've considered

Right now, we don't find out about regressions in our Sample Code until the change has been merged into master in this repo -- we can do better.