fix(akonadiserver): Use xdg_data_home and xdg_config_home as variable.

Summary:
As the source of most of the directories are created from XDG_DATA_HOME
and XDG_CONFIG_HOME we should also reflect this in the AppArmor
profiles with variables.

Test Plan: run Akonadi with AppArmor enabled.

Reviewers: cgiboudeaux, kde-pim, dvratil

Reviewed By: dvratil

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D24541