Indicate the number of affected children by a particular parent

[nilmerg]

We want to show the number of affected children in case a parent has a problem.

It should look like this:

Notes

The monitoring module had such an indicator for services of a host in the past. It was dropped entirely in recent versions, due to technical limitations.

To bypass these, the actual number will be calculated by Icinga 2 in advance. This makes it a static value, as calculating it to represent the actual affected children is too expensive.

This also excludes the possibility for Icinga DB Web to apply role restrictions on it.

The description for this indicator then can be phrased like this: Up to <n> affected children

But it should only be shown in case there are actually any children affected, host_state.affects_children (column name not final yet) should allow to conditionally show it.

This indication then has the only effect of making the element stand out in lists, so that is visible at first glance and the user can click on it, to then analyze the incident more closely.