Limit relationship to only certain valid item ids

[Letme]

The request is to output a warning or even an error when item uses a relationship to another item which is not accepted.

As example, we have relationship parent,child. Then we have item1 ITEM_PARENT-ITEM1 which has child relationship to item2 ITEM_CHILD-ITEM2 (valid) and then we have item3 which is ITEM_CHILD-ITEM3 which as child relationship to ITEM_PARENT-ITEM1. In this case item3 relationship child should trigger a warning/error as only parent relationship should be allowed.

Proposed implementation is to allow only certain regex to be part of the relationship like

relationship: parent,child
relationship_validation: ITEM_PARENT-*,ITEM_CHILD-*

FYI: @dryodon

[JasperCraeghs]

This is an shortened configuration to serve as an example. It should only contain forward relationships:

{
    'SYSRQT': {
        'depends_on': 'SWRQT',
        'validates': 'SWQTEST',
    },
    'SWRQT': {
        'depends_on': 'SWRQT|SWARCH',
        'validates': 'SWQTEST',
    },
    'SWARCH' {
        'depends_on': 'SWDESIGN',
        'validates': 'SWITEST',
    },
    ...
}

If a relationship that is not documented in this configuration dictionary is detected in the documentation, a warning shall be produced, i.e., this configuration shall be exhaustive. Or shall it be configurable to be non-exhaustive as well @Letme ?