Allow Jackson's serialization inclusion to be configured via the env

This commit adds support for configuring an ObjectMapper's
serialization inclusion using the environment via the
spring.jackson.serialization-inclusion property. The property's value
should be one of the values on the JsonInclude.Include enumeration.
Relaxed binding of the property value to the enum is supported. For
example:

spring.jackson.serialization-inclusion: non_null

Closes gh-2532

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -142,6 +142,7 @@ content into your application; rather pick only the properties that you need.
 	spring.jackson.mapper.*= # see Jackson's MapperFeature
 	spring.jackson.parser.*= # see Jackson's JsonParser.Feature
 	spring.jackson.serialization.*= # see Jackson's SerializationFeature
+	spring.jackson.serialization-inclusion= # Controls the inclusion of properties during serialization (see Jackson's JsonInclude.Include)
 
 	# THYMELEAF ({sc-spring-boot-autoconfigure}/thymeleaf/ThymeleafAutoConfiguration.{sc-ext}[ThymeleafAutoConfiguration])
 	spring.thymeleaf.check-template-location=true