separated e2e test to remove test-only/circular module dependency to pop

[sio4]

Separated e2e test to remove test-only/circular module dependency to pop.

The circular dependency was introduced by #94 and it made fizz hard to manage its module dependency. Checking if this workaround works.

The dependency graph of the previous versions:

It will become:

Some checking points on this e2e test:

• the test is a static test without any autogenerated files during the test
  • in most situation, I guess the test result will be the same every runs if the developer did not regenerate migrations
  • so it does not work as a gatekeeper
• not sure if fizz is a good place for the e2e test.