Add Per Role Toggle for Default Volume Mappings

[YozoraXCII]

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Describe the problem
When using Deemix, the default Download Path is /downloads, which is mapped as part of the common volumes that all containers receive.

When a custom download path is entered in the GUI, it is wiped on container reboot - reverting back to /downloads.

At present, there is no way for me to map /downloads to another location on my system for that specific container, so every time my container is updated/restarted I need to go in and amend the path.

Describe any solutions you think might work
A role toggle to allow me to disable or override the common volume mappings.

Additional context
Discussed in Discord here: https://discord.com/channels/853755447970758686/1212124669554200606