🍒 applets/batterymonitor: Warn about higher energy consumption when blocking sleep

EU Regulation 2023/826 requires connected devices to auto-suspend after at most 20 minutes. The user may disable this but a warning has to be presented when they do.

CCBUG: 501057

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String freeze exception has been granted: https://mail.kde.org/pipermail/kde-i18n-doc/2025-March/002663.html