feat: add allow only option

[neodmy]

Description

• Add allowOnly option to allow only package licenses complying with the provided list
• Add a function to check scan inputs
• Update error messages

Related Issue

#24

Motivation and Context

Users may want to be more strict with the licenses of the packages in their projects. By using allowOnly, they can make sure only packages with certain licenses are allowed.

To achieve the same behaviour with the failOn option, they would need to provide all the SPDX licenses available except the ones they'd like to be banned. With allowOnly, they just need to supply the licenses they need their packages to comply with.

How Has This Been Tested?

I've added tests for the checkArgs util and scan use cases with allowOnly

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[inigomarquinez]

Great job, @neodmy !

One question before approving it. 🤔