Support different JsonMapper for different datasources

[robsigler]

Feature description

I have a use-case where it would be helpful for Micronaut to support having different JsonMappers for different datasources. Specifically, I need to use a different JSON serialization strategy for a DataType.JSON field I am persisting with Micronaut Data JDBC datasource than the default JsonMapper that I use to serialize my API's HTTP responses, so if I could define a @Named JsonMapper and then configure a datasource to use a specific named JsonMapper instead, that would solve my problem!

[altro3]

@dstepanov It would be nice to support it not only in micronaut-data. I think, better to add this functionality in core module and also add support custom object mapper on http client level. Maybe it's better to add configuration like http client by EachProperty annotation like this:

mappers:
  default:
    ...
  client1:
    ...
  client2:
    ...
  ds:
    ...

And this feature will be usefull without http clients and datasources. Sometimes you need multiple ObjectMappers just for business logic