Refactor required string dup in 3x runtime converter

Types and Provider implementations must not mutate the parameter values of a resource. In Puppet 6.0.0 it is more likely that the parameters of a resource will have frozen (i.e. immutable) string values and any type or provider that directly mutates a resource parameter may fail. Before Puppet 6.0.0 every resource attribute was copied to not make application break even if they did mutate. Look for use of {{gsub!}} in your modules and replace logic with non mutating version, or operate on a copy of the value. (All modules authors of modules on the forge having this problem have been notified).