Add missing permission strings

GS_APP_PERMISSIONS_SYSTEM_BUS and SESSION_BUS only had "..."
placeholders as explanation text.
1 job for <span class="ref-name">wip/kalev/missing-permission-strings</span> in 15 minutes and 44 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #231870
build-gnome-software

00:15:44