WACZ Spec: Better metadata about software used to create the WACZ

[ikreymer]

Add a way to include additional metadata about how a particular WACZ file was created, in case some does want to try to recreate the result, and the data is still available (though no general guarantees on reproducability are possible)

We do have the software field in datapackage.json, but perhaps that should be expanded.

• For Browsertrix Crawler, does it make sense to include the hash of the image?
• For Browsertrix Crawler, should we also include the full crawl config + crawl params?
• For ArchiveWeb.page, probably just the version? (Could also include the git commit)
• For py-wacz, probably also just the version? (Could also include the git commit)

Are there any existing standard approaches to 'software citation' for this that we could extend?