Add model system boundary

[LillyG901]

Description of the issue

The ontology currently contains system as a term, but no way to explicitly reference the boundary that separates it from the rest of the real world. This is a term needed for modeling uncertainties, more specifically the location of an uncertainty within a model (that models the system).
See issue #1829.

Ideas of solution

The term should be defined similarly to how it is described within this paper to properly work in the needed context. The class should be related to system.

Workflow checklist

• I discussed the issue with someone else than me before working on a solution
• I already read the latest version of the workflow for this repository
• The goal of this ontology is clear to me

I am aware that

• every entry in the ontology should have a definition
• classes should arise from concepts rather than from words

[madbkr]

Maybe adding the proposed definition here would be good. This is the current draft from @LillyG901

A system boundary is a model component that separates aspects of the real world that are included in the model from those that are not.

[LillyG901]

System boundary is the demarcation of aspects of the real world that are included in
the model from those that are not included. The system boundary is often determined
by the problem and the chosen framing (Walker et al., 2003). This location is called
‘context’ by Walker et al. (2003), while Petersen (2006) includes it under
‘conceptual model’.

is the definiton given within the paper

[stap-m]

I like the definition proposed.
The cited part suggests a logical relation such as 'system boundary' 'part of' 'conceptual model'. We should keep that in mind for #1952

[madbkr]

I like the proposed definition too. It seems to capture everything necessary.

[LillyG901]

During a discussion with @stap-m and @ColinHDev it was suggested to change the term to model system boundary for clarity.

[LillyG901]

If there are no further comments on this proposal, I would open a PR to add:

A system boundary - is a model component that separates aspects of the real world that are included in the model from those that are not.

after PR #1945 has been merged.