Add ability to mount volumes

[stone-w4tch3r]

Is your feature request related to a problem? Please describe.
I use toolbox in fedora silverblue. I want to install dotnet sdk into a toolbox and than expose it to host for using with IDE. I can call dotnet command using toolbox run, but I also need access on host to files of sdk that are installed into /usr/lib64/sdk/dotnet.

Describe the solution you'd like
This can be solved with volumes: I will create /home/user/dotnet:/usr/lib64/sdk/dotnet mount and use it in my IDE

Describe alternatives you've considered
I tried to mess with podman:

• add volume to an existing toolbox (not possible)
• create a new container from toolbox image (but to be usable toolbox must configure this container first, and I didn't figure out how to do this)
• commit existing toolbox container and run a new one from this image (throws errors on starting and fails)

Additional context
There was a PR #100 that can support this, but it was closed without implementation many years ago