Add support for "JSON" type in the generators

[crimson-knight]

Currently in v1.3.2, if you try using a generator with a column type of json you will get an error.

So this:

amber g model person custom_attributes:json

Will produce an error similar to:

2023-05-19T12:55:40.539553Z   INFO - generate: Generating Amber::CLI::Api
Unhandled exception: type json not available (Exception)

Let's add support for that. It may also require some changes to Granite to ensure that the JSON and JSONB column types map properly to JSON::Any or some kind of serializer.