Explanation
Box 1: PackageTemplate.cs
Define custom code for your package in the PackageTemplate.cs file.
Box 2: ImportConfig.xml
The sample data and some flat files for solutions specified in the ImportConfig.xml file are imported before the solution import completes.
Box 3: Copy Always
Set the Copy to Output Directory value to Copy Always. This ensures that your file is available in the generated package.
Reference:
https://docs.microsoft.com/en-us/power-platform/alm/package-deployer-tool