Generate summary page linking all timelines.

[schultek]

After generating timelines (e.g. by running all tests with timeline mode all) I store them as artifacts in the ci. I'd like to have a single entrypoint to view all available timelines.

Proposed feature:

A cli command that generates a new index.html in the timeline folder that shows a list of all timelines and links to their respective html file. Optional: a short summary of each, whether the test was successful, a preview of the screenshots.