For the nuget package version, using the AssemblyInformationalVersion attribute in AssemblyInfo instead of GitVersion

- Updated Pepita to version `1.21.2.0` to include the fix for using the `AssemblyInformationalVersion` attribute
- Updated the CreatePackage task to not use GitVersion, instead supply the version in `AssemblyInfo` instead

@andreasohlund @SimonCropp - please review.