[IMP] base: user defaults groups performance

Improve the performance of the default method for user groups by avoiding a `ref` call,
using the group in cache instead.

Calls to ref always trigger one SQL query to verify record still exists
This means that creating 10k user would trigger 10k queries only for the default.

X-original-commit: e67efb88338ef669059591728e7722fe1dff4bf0