Add integration tests for a multi-module Gradle project

# Task Description

We need to add some more tests under the [idempotence-gradle-integration-tests](https://github.com/carlspring/idempotence/tree/master/idempotence-gradle-integration-tests) that cover a multi-module set up.

# Open Questions

# Notes

# Task List

The following tasks will need to be carried out:
* [ ] Create a new test Gradle multi-module project.
* [ ] Make the necessary adjustments to the scripts.
* [ ] Implement tests.

# Useful Commands

# Incurred Costs

# Task Relationships

This task:
* Is a sub-task of:
* Depends on:
* Is a follow-up of:
* Relates to:
* #10

# Resources

# Useful Links

* [Idempotence: Documentation](https://carlspring.github.io/idempotence/)

# Points of Contact

* @carlspring

Start by reviewing the existing tests and scripts under idempotence-gradle-integration-tests, and compare the related work in issue #10. Done means the directory contains a multi-module Gradle test project, the scripts support it, and integration tests cover the multi-module setup.

Written by the indexing model from the issue text.