Werk #14172: BI: Fixed broken host_search/child-with filtering

The host search option "The found hosts' (with child filtering)" was broken since the BI rework 2 years ago. Any attempt to save this setting lead to an exception.

The fix for this problem required a small change in the API specification for the refer_to field

• "refer_to": "host" -> "refer_to": {"type": "host"}
• "refer_to": "child" -> "refer_to": {"type": "child"}
• "refer_to": "parent" -> "refer_to": {"type": "parent"}
• "refer_to": {was broken} -> "refer_to": {"type": "child_with", "conditions": {..}}

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