[FEAT] version-comparator: avoid manual croping of image to generate gif

[tbouffard]

Is your feature request related to a problem? Please describe.
Today, we do snapshot with the playwright default viewport size. We fit the B.2.0 content in the page but it generates blank area that we needs to crop manually when generating the zip.
This is documented in https://github.com/process-analytics/bpmn-visualization-tools/tree/v0.2.0/bpmn-rendering-from-version-to-version#tips-to-generate-videogif-from-screenshots

Describe the solution you'd like
Find the right viewport size that avoid us to crop the resulting screenshot.
The initial implementation of the "miwg-test-suite" tool use custom viewport. Its width/height ratio can be used as a starting point to configure the viewport here.

Additional context
WARN: the video generation procedure should be updated as well as it currently assume that the viewport width is 1280px