Default acceleration mode option is none of the 3 nvidia settings option

As stated on bug #1876052, the default acceleration mode option is none of the 3 nvidia settings option.

It’s displayed as "Performance mode" when you launch it for the first time, however:
- default launch is Intel (so no performance mode)
- there is a "Use dedicated card" option (which shouldn't be displayed in "Performance mode" and this one is triggering software acceleration)
- nvidia settings is only displaying that tab, and selecting another mode, then selecting it back this one after reboot will display all other tab options, so nvidia settings knows that the default setting is different from Performance mode.

It seems nvidia settings is only showing the On demand option for cards that support it. I suggest thus that our default selection represents a better option for our users:
- If the card supports On demand acceleration -> select that by default
- If the card doesn’t support On demand acceleration -> select Performance mode by default
- Remove the current "weird" status it's currently on by default.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: nvidia-settings 440.64-0ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-28.32-generic 5.4.30
Uname: Linux 5.4.0-28-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 30 09:43:31 2020
InstallationDate: Installed on 2020-04-24 (5 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: nvidia-settings
UpgradeStatus: No upgrade log present (probably fresh install)