Default statistic custom field
Introduction
In Portal statistic, when user add new chart, statistic filter will
displays default 5 custom string fields CustomVarCharField1 to
CustomVarCharField5, you can customize them by your own custom
string fields.

Customization
Create an override which overrides sub process
createDefaultStatisticCustomField() in DefaultStatisticCustomField.mod process in PortalKit. This sub process
return a list of custom string fields. Follow instruction to create
default custom fields.
