Also, use ISO639 languages in some places.

Also, some openalex fixes.

IF NOT EXISTS makes sense only when you provide the name of the index.

This important commit introduces the 'DbCmd' constraint set, allowing DB
functions to require only a connection pool and some `GargConfig`.

Merge remote-tracking branch 'origin/239-readme-test-reinstall-project-with-cabal-and-update-the-readme-file-2' into dev

This is to prevent accidental updates of hyperdata with other JSON
structs.