[JENKINS-72371] Improve Nodemonitor configuration #18822

The configuration of node monitors is working strange I think.

Before each monitor is a checkbox. The purpose of the checkbox is to disable that the monitor takes agents offline. But this is not really intuitive. At first glance one might think it will disable the monitor completely and hide it from the computer overview page. But this is not the case. For Monitors, that only have informational character like the architecture monitor this has the only affect that the ordering of the monitors on the computer overview page changes.

And for monitors that have configuration it has the negative side effect that the configuration is not saved. E.g. I want to have the free disk space configured to 10GB but I don't want that the monitor takes my agents offline. This is not possible at the moment.

This lead to the java version monitor (from the versionscolumn-plugin) implement its own checkbox to take agents offline.

The configuration should be changed so that for monitors that can take agents offline, there is an additional checkbox ignored and it is ensured that the configuration for each monitor is always saved.

Optionally making the monitors sortable might be also considered.