Werk #16089: etherbox_smoke: Fix default behaviour and remove predictive levels option

The check plugin etherbox_smoke monitors smoke sensors of Etherboxes. Werk 14664 introduced configurable levels for this plugin. However, this accidentally changed the default behaviour of the plugin. Before werk 14664, the plugin reported OK if no smoke was detected and CRIT otherwise. With werk 14664, by default, the plugin always reported CRIT, even if no smoke was detected.

As of this werk, the old default behaviour is restored. Furthermore, a new configuration option is added. Users now have two alternatives for configuring the behaviour of the plugin: Users can either specify two monitoring states for the two cases "smoke detected" and "no smoke detected", or, alternatively, users can specify WARN and CRIT thresholds on the smoke level.

Finally, this werk removes the option to configure predictive levels for this check plugin, which was also added by werk 14664. Using this option lead to a crash. Already existing configurations will automatically be migrated to the default behaviour mentioned above.

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