py-wacz: Add a way to list pages in the WACZ

[ikreymer]

Something that could help with testing browsertrix-crawler is a way to list pages in the WACZ, maybe something like:

> wacz extract pages --url
https://example.com/

Not sure if its generally useful, outside of testing, but may be? Could allow listing just URL, or all the other fields.
Of course, easy enough to just unzip pages/pages.jsonl so not sure if we want this.
Just opening this to keep track.

(Extracting URLs from index could be another feature later)