add new validator - DanglingCondition

[nasbench]

Description

This PR adds a new validator - DanglingCondition

Motivation

In certain edge cases, a sigma rule author might reference an unknown detection definition from the condition in the form of 1 of something. Example:

title: Test
status: test
logsource:
    category: test
detection:
    selection:
        field1: val1
    filter_main_1:
        field1: val1
    filter_main_optional_1:
        field2: val2
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*

Currently pySigma gracefully handles the conversion without error but this might lead to confusion in certain tools and the semantically the rule contain an "error".

Solution

This PR adds a new validator that is very similar to the DanglingDetection. The difference being the use of the fact that when a ConditionSelector calls resolve_referenced_detections it will return an empty set if the detection definition doesn't exist (i.e match any patterns).

[frack113]

LGTM