I just got to this myself, and the solution is fairly simple - just add the config as a bind mount:
-v '/mnt/user/appdata/quartz_builder/quartz.config.ts':'/quartz/quartz.config.ts':'ro'
So, in essence:
Create your `quartz.config.ts` file somewhere.
Edit the container in Unraid.
Click "Add another Path, Port, Variable, Label or Device" and create a new path.
Set `/quartz/quartz.config.ts` as the "Container Path"
Set the path where your config file is as the "Host Path", e.g. `/mnt/user/appdata/quartz_builder/quartz.config.ts`.
For safety, set "Access Mode" as RO.