Add the ability to create a callout line on model builder labels

[DuncanHornby]

This is a cosmetic idea for model builder. We can add labels to the model builder canvas to help explain our model but it depends entirely on where you place the label to what it is referring to. Now some labels may be a general model level note but many labels might be explaining a specific step in the model.  I would like to see the ability to create a call out line  that you can draw so the label is pointing the thing that its  referencing. I don't think it needs to be "connected" to a model element, although snapping to an element would be nice.

I envisage something like the green line below:

Recently I saw a colleague using FME and FME does exactly what I want, we can see that it creates a callout line as shown in the example below

[LR2]

Customizable bubbles like in FME would be nice.