Add support for a configuration file for the CLI

[masayag]

The purpose of the configuration file is to customize some decisions taken by the CLI itself.
e.g. the default (and only) image being used to run workloads is hard-coded in code.
Additional configuration items:

• Workloads naming
• Configuration of k8s cluster

toml file will be a good fit here by introducing sections per workload, device and k8s.