Add a startup mode that enables using env variables instead of CLI arguments

[nektro]

No description provided.

[riptl]

I did this with cobra + viper in od-database-crawler, maybe it helps.

It supports config via yaml, json, flags and environment.

e.g. --output.log = {"output": {"log": "value"}} = $OD_OUTPUT_LOG

[nektro]

So, this issue was created in order to help enable #27, however they can be used separately. I could add a function that was similar to the following (I'll see if this is what viper does)

func getProp(name string) {
    if args.Has(name) { return args.Get(name); }
    if env.Has(name) { return env.Get(name); }
    return default;
}

[riptl]

@nektro Viper is a key-value storage. If it doesn't find anything in-memory, it'll look in environment.
So it essentially does the same, I guess.