Search changelog files in monorepositories

[Clement134]

Description

Detect monorepositories and search changelog files in the packages subfolders.

Motivation and Context

In a monorepository changelog files aren't located at the root file structure, they are usually find in the subfolder (in the packages folder) corresponding to the module. This PR should fix #183.

Types of changes

• [ ] Bug fix (fixes an issue)
• [x] New feature (adds functionality)

Does this introduce a breaking change?

• [ ] Yes
• [x] No

How Has This Been Tested?

Tested manually with multiple monorepositories (rollup, istanbuljs, aribnb, typescript-eslint). Unit tests adapted with this new use case.

Checklist:

• [ ] My change requires a change to the documentation.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[Clement134]

All tests are good, this PR will be released in the next release.