dApp: add end-to-end tests for quick pay functionality

[weilbith]

Description

Due to time pressure for the PayWall MVP and the complexity of this task, I'm opening this issue to actually write the end-to-end tests for the feature in #2882 . While there are extensive unit tests for it, we must also have end-to-end tests. As illustrated in the image at the issue, there are 7 cases to be handled. 5 of them are only implemented yet. It requires some planning to figure out how we can find a setup and order or quick payments to test all cases. We probably need a fourth Raiden node in the end-to-end environment for this.

Acceptance criteria

Tasks

• [ ]