[Feature Request] Implement mapping single-file volumes, just as docker compose commandline can

[fiveangle]

Is your feature request related to a problem? Please describe

Lots of docker image maintainers use single-file volume mapping for their config files (filebrowser, timothyjmiller/cloudflare_ddns, so so many others). This prevents deploying these images using the direct Stacks editing feature of Portainer. There is no error, but the container cannot access the file.

Describe the solution you'd like

Allow single-file volume mapping to function as it does with docker compose example:

volumes:
      - /var/lib/docker/volumes/cloudflare-ddns/config.json:/config.json

Describe alternatives you've considered

I've attempted to start the stack once, stop it and go remove the directory Portainer created with the mapped filename, replacing it with the required file, then restart. But even in that instance, the container cannot access the file.

Additional context

No response