[SDK] Support string values in min/max replicas

[GiladShapira94]

https://jira.iguazeng.com/browse/ML-2819

[liranbg]

I'd move the verification + assignment under a common helper, and set it to be

def as_number(field_name, field_value)
if (
            isinstance(field_value, str)
            and not field_value.isnumeric()
        ):
            raise ValueError(f"{field_name} must be numeric")
return int(field_value)

and then, use it from anywhere, without repeating the logic

DRY

[GiladShapira94]

@liranbg - fixed