PDCL-6855 Add checkboxes to return `undefined` values when users need it.

[dompuiu]

Description

Add a checkbox that will allow the user to decide if the data element needs to return a value or not. Allow also the conditional value to be an empty string. Emit numbers values as Number inside the settings object.

Related Issue

https://jira.corp.adobe.com/browse/PDCL-6855

Motivation and Context

https://github.com/adobe/reactor-extension-core/issues/62

Screenshots (if appropriate):

Types of changes

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

Checklist:

• [x] I have signed the Adobe Open Source CLA.
• [x] My code follows the code style of this project.
• [ ] I have updated the Experience League documentation for the Core Extension
• [x] All tests pass and I've made any necessary test changes.
• [x] I have run the extension sandbox successfully.