[Task] Add "warning"-level validations

[atextor]

Is your task related to a problem? Please describe. There are corner cases in modeling that indicate something went awry but are technically not invalid. One example is using a bamm-c:Either with both of its bamm-c:left and bamm-c:right pointing to the same Characteristic. This can and should be checked by the validation rules so that a model validator can give helpful hints.

Describe the solution you'd like

• Create a list of explictly "discouraged modeling practices". This should be part of #68.
• For each of the discouraged modling practices, create a SHACL shape with a severity of sh:Warning

Describe alternatives you've considered The alternative would be to add checks only on the tooling level. However, this would mean that different tools could show different types of warnings, which is not helpful.

[BirgitBoss]

2022-04-21 SDS Meeting: Introduction of a Warning level in validation is appreciated. Maintenance of discouraged modeling practices might be difficult when BAMM model evolves or at least more effort: all rules needs to be checked whether still valid. It is difficult to decide: when exactly something should throw warning? We do not have clear rules...