SourceSideValidations should be able to generate stats.csv for migration

[bill-long]

Typically, Export-ModernPublicFolderStatistics.ps1 is used to generate stats.csv, which is then used to generate the folder map for migration to EXO. However, that script is not as robust as SourceSideValidations. Errors can cause it to fail without retry and produce no data.

SourceSideValidations already collects almost enough info to generate the stats.csv itself, and it does so with decent error handling while using parallel jobs for better performance. We should add the capability for SSV to generate the stats.csv to solve scenarios where Export-ModernPublicFolderStatistics is not working.