Create test packages that simulate malicious behaviors we want to catch

[elainechien]

Having test packages will aid development and testing of new functionalities for package analysis since we can do more end to end testing on specific behaviors we want to catch. If we find reports of packages with malicious activity that package analysis missed, we should try to simulate that behavior in these test packages and add support for detecting those behaviors. The initial test package will be created in python, but we should consider creating test packages for multiple ecosystems.