improve config parsing to accommodate type casting and validation rules

[msramalho]

As it stands the logic to handle the configs() method of each Step (like Archivers, Enrichers, ...) does not cast int/float/bool and uses only strings. Likewise it's proven quite useful to specify validation rules in the configs rather than relying on the init method of each Step to do so.

This issue is on adding both of those configuration parsing mechanisms and refactoring existing Steps that are doing internal casting/validation.