- add validation as extra step after migration
- add missing json struct tags to new v1alpha3 config fields
- add unit tests
- add missing `omitempty` tags to configs to avoid (un-)marshalling issues
- drop `string` type for `time.Duration` type field in JSON Schema (doesn't work properly sometimes due to broken handling of time.Duration as per https://github.com/golang/go/issues/10275)
