[Feature] Desktop mode: Software Update Defaults

[thegreatGreenstar]

Currently (at least according to clicking the defaults button), Desktop mode starts off with Software updates set to:
Update software: [Manually,Automatically]
Notification frequency: [Daily,Weekly,Monthly,Never] (This setting is replaced by Update Frequency when Automatic updates are enabled)
Apply System updates: [After Rebooting, Immediately]

However, this introduces additional requirements for user action.
Therefore I propose that the Desktop mode defaults be changed to the following:
Update software: [Automatically]
Apply System updates: [After Rebooting]

Explanation:
Automatic software updates as suggested reduces time spent updating things, and users could manually update if so desired but this usually isn't a need or requirement.
All options for Update frequency have their own merits and downsides, so I do not suggest anything here definitively, and it can be left to current default.
SteamOs already requires rebooting after updating to apply updates when done in gaming mode, this setting should be set to after rebooting for parity which reduces possible conflicts.

[oSoMoN]

Note: regarding system updates, the setting is irrelevant for SteamOS, given the architecture of the system (immutable with an A/B partition scheme): a reboot is necessary to "apply" an installed system update, i.e. to switch the current partition set.

I'll work on a patch to hide this setting.

Defaults for the other settings can still be discussed here.

[oSoMoN]

The patch to hide the setting for system updates landed upstream, and will be cherry-picked in an upcoming version of SteamOS.