Making sure that it runs and not segfaults

This will output a warning if an invalid value is requested. The goal is to avoid
implicit conversion which might result in a zero-int value.

By using an enum we have a central place to provide docs for the most
common actions/restrictions. Also consumers can pass in type-safe enum
values instead of potentially undocumented strings that might contain typos.

Also it is better documents is a value is supposed to be authorized using
KAuthorized::authorize or KAuthorized::authorizeAction, in the case of "shell_access"
this was mixed up from time to time.

Considering that we do not want the parameter for the methods to become too long
I have deliberately decided against using `enum class`. Also we don't have
and usecases for the binary operators in combination with the newly added enums.

Task: https://phabricator.kde.org/T11948

This will become especially useful when moving state data from the config file
to a dedicated state data file.

Task: https://phabricator.kde.org/T12549

Otherwise we force consumers to use the config location for state data,
which is what we are trying to avoid.

Task: https://phabricator.kde.org/T12549