enh(build) Add Subresource Integrity digests for CDN builds

[joshgoebel]

Makes the following changes:

• Builds a DIGESTS.md file for CDN builds with simple instructions
• includes example and list of all digests for all files
• Updates release script to move DIGESTS.md to root of cdn-asset repo
• Update README.md to mention SRI and link to DIGESTS.md

IE, we don't actuall publish DIGESTS.md to the CDNs, but it's available
in the repo for anyone who wants to use it to know what the digests are.

Changes

Checklist

• Added markup tests, or they don't apply here because...
• Updated the changelog at CHANGES.md
• Added myself to AUTHORS.txt, under Contributors

[joshgoebel]

It might be nice to include digest more prominently in the README.me but then we get into reproducable build issues (I'd hope they are, but who knows - right now the canonical version is whatever is build by GHA during release) plus needing some automated way to keep it up-to-date all the time... plus what is the correct digest information for "master" anyways when it's always changing?

Seems better to me to always keep this information in a version keyed resource, like cdn-assets. Doubly so since we already have the mechanism to do this easily. :)

[allejo]

I think I'm going blind, where is ./tools/templates/DIGESTS.md located?

[joshgoebel]

Better?