dhparam not being persisted outside of the container overlay fs

[leepfrog-ger]

Is your feature request related to a problem? Please describe.
When recreating the stack (e.g. by running docker compose down / bin/production.sh down) it removes the overlay volume and therefor also the dhparam file that was generated.
Depending on the scenarios, troubleshooting etc. this can happen often enough for it being annoying, since, depending on the hardware it can take quite some time for the process to finish.

Describe the solution you'd like
Persist the generated dh params somewhere outside of the container (bind mount?)