Apply checkstyle rule to ensure that private and package private
classes do not have unnecessary public methods. Test classes have
also been unified as much as possible to use default scoped
inner-classes.
Closes gh-7316
Prior to this commit, the application properties listed in the reference
documentation would be manually managed and updated.
This commit adds a new `spring-boot-configuration-docs` project that
extracts that information from the available JSON metadata and writes
Asciidoctor tables ready for inclusion in the reference documentation.
The `generateConfigurationPropertyTables.groovy` is using this library
and configures the sections and how namespaces should be organized.
Fixes gh-8237
