Support navigation traces for the whole frameset

[ka3de]

Currently, after #1100, traces are generated in order to represent the actions performed by k6 browser and the state changes in the page as a result of these. One of the main actions that are represented in the traces is the navigation action, which is generated when a frame navigates (see FrameSession.onFrameNavigated).

The problem is that, #1100 only generates navigation traces for the main frame.

The goal of this issue is to decide if and how the rest of the frames in the frameset, beyond the main frame, should be represented in the traces generation.