Let developer set App Store region for UpdateAvailableInsight

[Rubenfer]

Hi,

just started using this library in one of my apps and noticed the report doesn't includes the update available smart insights because my app is only available in Spain and it tries to retrieve metadata from Brazilian App Store. In this PR I include an optional parameter to set the iTunes region in the create report method. Also including the option to set custom report filename.

Congratulations for this great package.