Change default serialization of time types

[shawkins]

Given the recent changes to use jackson to produce the crd types for java / javax classes that have jackson overrides, we should use mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS) by default - that will generate the most expected from of the crds.

This could be considered a breaking change, but previously the mapping that was generated was object and not usable at all, so we should be free to make this change as a bug fix.

If there are objections to making this change in 6.x, the new crd generator will allow for an ObjectMapper to be passed in that has this configuration.