Auto-generate the "Common application properties"

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

spring-boot-project/spring-boot-tools/pom.xml

@@ -17,6 +17,7 @@
 	<modules>
 		<module>spring-boot-antlib</module>
 		<module>spring-boot-autoconfigure-processor</module>
+		<module>spring-boot-configuration-docs</module>
 		<module>spring-boot-configuration-metadata</module>
 		<module>spring-boot-configuration-processor</module>
 		<module>spring-boot-gradle-plugin</module>