Consistent values parsing

[sl4vr]

There is inconsistency now:

• values from yaml files are parsed into sage types, e.g. str, int, bool
• values from cli arguments and env variables are always str and require type cast.

AFAICS config parsers usually use strings and cast values when they are fetched from config, e.g. configparser, confuse.

But k8t could handle values from cli arguments and env variables same way as it's done with the ones from yaml files.