Cannot set snake case hot/cold repo options via environment variables

[k9withabone]

I'm trying to set the account_key hot/cold repository option for the OpenDAL azblob backend via an environment variable so that I can load it from a systemd credential. This seems to be impossible at the moment as RUSTIC_REPO_OPTHOT_* and RUSTIC_REPO_OPTCOLD_* variables are converted to kebab case. #1081 allowed for setting OPENDAL_* variables as snake case, but those options then apply to both the hot and cold repository.

Rustic version: 0.9.5

[aawsome]

Thanks for opening this issue @k9withabone
I created #1392 which should solve this.