INT-3427: Add `JsonNodeToStringConverter`

JIRA: https://jira.spring.io/browse/INT-3427
Because we register with this change the `ToStringFriendlyJsonNodeToStringConverter` for our `ConverterRegistrar`, which causes the `CustomConversionServiceFactoryBean` registration as well. See `IntegrationRegistrar` changes here and source code of `IntegrationConverterInitializer`, which "ate" the code from the former `ConverterParser`.