KCM: Provide a default action for "Suspend session" configuration
When checking "Suspend session" in System Settings -> Energy Saving, a default timeout of 10 minutes is provided. However, the user must choose an action such as suspending to RAM, locking the system or shutting down for the setting to actually do anything.
This MR sets a default action in the configuration UI if the setting is missing from powermanagementprofilesrc so that enabling "Suspend session" is enough for an action to happen. I have chosen Sleep (suspend to RAM) as the default action if it's supported because it is the default setting when generating new profiles. If suspending to RAM is not supported, the default is to shut down the system.
Note that on systems that do not support suspending to RAM (or are virtual machines) "Suspend session" is not enabled by default. Therefore, I believe this behavior is in line with existing powerdevil defaults.