Use Case Diagram: Allow comment notes for extends relationships

[stephanlukasczyk]

Is your feature request related to a problem?

Use case diagrams can have, among others, extends relationships between two use cases. UML allows to make these extends relationships conditional by adding a note to them. Unfortunately, the editor does not allow to add such a node.

Describe the solution you'd like

I would like to have a way to add such a note to an extends relationship in an easy way. I see two possible solutions: either one can add them as an optional free text when editing the relationship (similar to what the simple association allows), or one has to have a dedicated graph element for the note. An example of the desired result can be seen at https://www.uml-diagrams.org/use-case-extend.html.

Describe alternatives you've considered

Currently, our students try to emulate the note with the existing box element or by providing a textual note in the explanation text box. While these approaches work, they do not follow the syntax of UML, can be misleading while grading, or even missed while grading.

Additional context