[FEAT] Display Association related to Pool

[csouchet]

For now, we only support the Association defines in the process tag and subProcess tag (see #397).

In the BPMN specification, the association can be defined in the collaboration, to represent a Association related to Pool.

Need to update the unit tests for the JsonParser, for the association and the incoming/outgoing (#2521).

[tbouffard]

Notice that we already support some associations attached to a Pool. See #2588 (comment)
In the mentioned example, the "association" is not defined in the "collaboration" but in a process (although it is linked to a participant/pool). This is why it already is rendered.