[Variable controls] Allow chaining for variable controls #238473
Description
Describe the feature:
Users want to use the output of one control as the input of another control.
Describe a specific use case for the feature:
The typical use case is a control that needs to be filtered down by another control
Example: If I only want to see the list of hosts for my selected services I can create a ?service control with the list of services FROM metrics-* | STATS by service.name and a ?host control that shows only the hosts for the selected service FROM metrics-* | WHERE service.name == ?service | STATS BY host
This is specially useful when the user has information in a control coming from a different index that the one used in the visualizations. They can create a variable control that can populate another control without affecting the whole dashboard which is something they cannot do today.