Build should fail if keys needed by public config aren't present, or otherwise warn us

[jbphet]

While working on #412 I found that I couldn't actually log out of the translation utility on ox-dev. I traced this behavior back to a missing key in the rosetta configuration file. The code that builds the public configuration file, which is in make-public-config-file.mjs, should cause a build failure or something that makes problems like these apparent. Silent failures make debugging tricky,