The Webmin MySQL or PostgreSQL module can provided to domain owner users. You or the domain owner may also choose to install phpmyadmin or phppgadmin, if that’s preferred or more familiar.
I’ve seen it mentioned occasionally, I guess, but most folks ask for phpMyAdmin, I guess because it’s been known for longer.
I’m partial to the Webmin MySQL module, but it’s just what I’ve always used. I find phpMyAdmin confusing. Never looked at Adminer, but it seems very simple to install, so it’s entirely plausible we could add it to Install Scripts.
The thing about it is, there is NO installing… You literally drop the file (single file) in place, and it just works.
If you want get a bit more fancy, you can also drop in one of the many stylesheets which is basically an override file causing the theme to adjust accordingly.
You can also add another layer to it, allowing you implement plugins with minimal effort.
But again, the core product itself is enough to be satisified for most people. Super powerful, yet simple!