fix: use external reference for Operation semanticId in aas

[gjavakhadze]

Description

Operation submodel elements generated by the AAS generator carried an invalid semanticId: a ModelReference whose first (and only) key had type Operation. This violates two constraints of the AAS metamodel specification (IDTA-01001):

• AASd-121: for References, Key/type of the first key must be one of GloballyIdentifiables; Operation is not.
• AASd-123: for model references, Key/type of the first key must be one of AasIdentifiables (AssetAdministrationShell, ConceptDescription, Identifiable, Submodel); Operation is not. Fragment keys such as Operation may only appear in subsequent keys (AASd-125/126/127).

This also made Operation inconsistent with every other submodel element generated from a SAMM model element (Property, Aspect, ReferenceElement, ...), all of which already emit an ExternalReference with a single GlobalReference key.

Fixes #998

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works