Add model implementation

[LillyG901]

Description of the issue

The ontology does not contain a way to separate the concept, implementation and the representation inside a computer of a model.
(related issues #1953, #1952)
This is a term needed for modeling uncertainties, more specifically the location of an uncertainty within a model.
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.

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

[stap-m]

@LillyG901 could you cite the relevant part of the paper for finding a definition, please?

[madbkr]

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

Model implementation is a model component that consists of the computer code used to represent the model.

[LillyG901]

Model implementation uncertainty deals with the uncertainties arising from the
implementation of the model in computer code. It addresses uncertainties related to
bugs and errors in the code, or hardware errors such as the well-known numerical
fault in early Pentium chips. Petersen (2006) calls this ‘technical model
implementation’; and Walker et al. (2003) call this ‘computer implementation’.

This is the definition within the paper

[LillyG901]

This issue will be further discussed in issue #1953 to better compare two similar terms in one place.