Spring Simplify overriding of default codec for Jackson 3 vs 2

At the moment CodecConfigurer.DefaultCodecs has settings for a default Jackson vs Jackson2 codecs, but the actual logic always prioritizes Jackson 3, so if both are present on the classpath, it is not possible to fix the use of Jackson 2 like in this commit.

We should simplify this to have only one setting for Jackson codecs. By comparison, the new HttpMessageConverters is even more generalized to have only one converter for JSON.