Rails 6.1 and error revamp

[yulgolem]

OK, we got a situation. In Rails 6.1 all the error objects got huuugely revamped and refactored, leaving next to none of previous behaviour ( proof ). And we got a whole lot of logic linked to the error object (e.g. in epp error https://github.com/internetee/registry/blob/master/app/models/concerns/epp_errors.rb). So ATM registry application is incompatible with Rails 6.1 and needs to be refactored.