Autoscroll before before archiving and take full-height screenshots

[pirate]

I've sumbitted a Chromium bug tracker feature request for adding a --full-page flag: https://bugs.chromium.org/p/chromium/issues/detail?id=854013

Hopefully it's merged, allowing us to screenshot the full height of pages, instead of limiting them to the config settings defined by DIMENSIONS.

[pirate]

This will be easy with user scripts the moment pyppeteer is merged in #177. Or if we switch to playwright it's also easy using playwright's --full-page flag. #51