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-docs/src/main/groovy/generateConfigurationPropertyTables.groovy

@@ -0,0 +1,79 @@
+import org.springframework.boot.configurationdocs.ConfigurationMetadataDocumentWriter
+import org.springframework.boot.configurationdocs.DocumentOptions
+import org.springframework.core.io.UrlResource
+
+import java.nio.file.Path
+import java.nio.file.Paths
+
+def getConfigMetadataInputStreams() {
+	def mainMetadata = getClass().getClassLoader().getResources("META-INF/spring-configuration-metadata.json")
+	def additionalMetadata = getClass().getClassLoader().getResources("META-INF/additional-spring-configuration-metadata.json")
+	def streams = []
+	streams += mainMetadata.collect { new UrlResource(it).getInputStream() }
+	streams += additionalMetadata.collect { new UrlResource(it).getInputStream() }
+	return streams
+}
+
+def generateConfigMetadataDocumentation() {
+
+	def streams = getConfigMetadataInputStreams()
+	try {
+		Path outputPath = Paths.get(project.build.directory, 'generated-resources', 'config-docs')
+		def builder = DocumentOptions.builder();
+
+		builder
+				.addSection("core")
+					.withKeyPrefixes("debug", "trace", "logging", "spring.aop", "spring.application",
+						"spring.autoconfigure", "spring.banner", "spring.beaninfo", "spring.config",
+						"spring.info", "spring.jmx", "spring.main", "spring.messages", "spring.pid",
+						"spring.profiles", "spring.quartz", "spring.reactor", "spring.task",
+						"spring.mandatory-file-encoding", "info", "spring.output.ansi.enabled")
+				.addSection("mail")
+					.withKeyPrefixes("spring.mail", "spring.sendgrid")
+				.addSection("cache")
+					.withKeyPrefixes("spring.cache")
+				.addSection("server")
+					.withKeyPrefixes("server")
+				.addSection("web")
+					.withKeyPrefixes("spring.hateoas",
+						"spring.http", "spring.servlet", "spring.jersey",
+						"spring.mvc", "spring.resources", "spring.webflux")
+				.addSection("json")
+					.withKeyPrefixes("spring.jackson", "spring.gson")
+				.addSection("templating")
+					.withKeyPrefixes("spring.freemarker", "spring.groovy", "spring.mustache", "spring.thymeleaf")
+				.addOverride("spring.groovy.template.configuration", "See GroovyMarkupConfigurer")
+				.addSection("security")
+					.withKeyPrefixes("spring.security", "spring.ldap", "spring.session")
+				.addSection("data-migration")
+					.withKeyPrefixes("spring.flyway", "spring.liquibase")
+				.addSection("data")
+					.withKeyPrefixes("spring.couchbase", "spring.elasticsearch", "spring.h2",
+						"spring.influx", "spring.mongodb", "spring.redis",
+						"spring.dao", "spring.data", "spring.datasource", "spring.jooq",
+						"spring.jdbc", "spring.jpa")
+				.addOverride("spring.datasource.dbcp2", "Commons DBCP2 specific settings")
+				.addOverride("spring.datasource.tomcat", "Tomcat datasource specific settings")
+				.addOverride("spring.datasource.hikari", "Hikari specific settings")
+				.addSection("transaction")
+				.withKeyPrefixes("spring.jta", "spring.transaction")
+				.addSection("integration")
+					.withKeyPrefixes("spring.activemq", "spring.artemis", "spring.batch",
+						"spring.integration", "spring.jms", "spring.kafka", "spring.rabbitmq", "spring.hazelcast",
+						"spring.webservices")
+				.addSection("actuator")
+					.withKeyPrefixes("management")
+				.addSection("devtools")
+					.withKeyPrefixes("spring.devtools")
+				.addSection("testing")
+					.withKeyPrefixes("spring.test");
+
+		ConfigurationMetadataDocumentWriter writer = new ConfigurationMetadataDocumentWriter();
+		writer.writeDocument(outputPath, builder.build(), streams.toArray(new InputStream[0]));
+	}
+	finally {
+		streams.each { it.close() }
+	}
+}
+
+generateConfigMetadataDocumentation()