Improve visualization and integration of the custom variables between Director and monitoring

[mcodato]

Use Case

In installations with numerous custom variables (exceeding 40), the monitoring interface can become cluttered and difficult to navigate. This is especially problematic in environments where multiple teams with different responsibilities and expertise levels access the monitoring module.

Currently, all custom variables are displayed in a flat, unorganized list. This not only overwhelms users with irrelevant information but also increases the likelihood of missing critical details relevant to their role. Furthermore, when variables are not categorized or collapsible, it becomes harder to discern which data belongs to a specific domain, leading to confusion and inefficiencies.

Proposal

Since version 1.11.2, the Director module introduced integration with the monitoring module and Icinga2 custom variables, displaying the related labels defined in the Director.

The same hook could be used to render variables while also considering the 'Data Field Category' and 'Visibility' properties specified in the Director.

At the same time _override_servicevars could also be collapsed or hidden, since it can grow a lot in some environments.

Users should be able to:
Navigate through categorized custom variables in the monitoring module.
Expand/collapse categories to focus on relevant information.
See only those custom variables that are set to be visible according to their settings in the Director.