Release v3.0.0

Stable release for Plasma 6 ! 🎉

Bug Fixes

• config: allow easier fix gpu index (675e308)
• graph: prevent cpu temp error (616c86e), closes #88

RC changelogs :

• https://github.com/orblazer/plasma-applet-resources-monitor/releases/tag/v3.0.0-rc.1
• https://github.com/orblazer/plasma-applet-resources-monitor/releases/tag/v3.0.0-rc.2
• https://github.com/orblazer/plasma-applet-resources-monitor/releases/tag/v3.0.0-rc.3