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