I wrote up the ghost-cli + MySQL bug

Over at https://github.com/TryGhost/Ghost-CLI/issues/1759, I carefully wrote up the bug in the current Ghost installation docs and suggested how to proceed.

I sniffed around in the code a bit trying to figure out how to fix it, but the untyped and comment-light code at https://github.com/TryGhost/Ghost-CLI/blob/main/extensions/mysql/index.js that takes in mysterious config and context objects was hard for me to make sense of at a glance; I would've had to spend a couple of hours reading and experimenting to make sure I understood all the ways that code can be called and how the values on the config object differ depending upon whether you've run setup before and failed or not or upon whether you're asking the installer to create a new database user for you or not. I figured it was better to leave it to the maintainers.