Have Sysbox pick up its configuration from a file

[ctalledo]

Sysbox currently picks up its config via command line parameters to sysbox-runc, sysbox-fs, and sysbox-mgr.

In addition to this, it would be good if Sysbox could pick up the configuration from a file. This is cleaner and will allow us to better deal with the number of config options (which are likely to grow over time).

Ideally it would be a single config file parsed by sysbox-mgr, from which sysbox-fs and sysbox-runc pick up their respective configurations. The config file could be in toml or json format (TBD).