Version layers configuration xsd

This commit provides a versioned xsd for the layers configuration of the
Maven plugin. The version starts at `2.3` to match with the Spring Boot
feature release in which this was introduced.

Closes gh-20663

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/build.gradle

@@ -50,6 +50,13 @@ syncDocumentationSourceForAsciidoctor {
 	}
 }
 
+tasks.withType(org.asciidoctor.gradle.jvm.AbstractAsciidoctorTask) {
+	doFirst {
+		def versionEl = version.split("\\.")
+		attributes "spring-boot-xsd-version": versionEl[0] + '.' + versionEl[1]
+	}
+}
+
 asciidoctor {
 	sources {
 		include "index.adoc"

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/docs/asciidoc/packaging.adoc

@@ -144,7 +144,7 @@ The following example shows what the implicit layer configuration described abov
 <layers-configuration xmlns="http://www.springframework.org/schema/boot/layers"
 					  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 					  xsi:schemaLocation="http://www.springframework.org/schema/boot/layers
-                      https://www.springframework.org/schema/boot/layers/layers-configuration.xsd">
+                      https://www.springframework.org/schema/boot/layers/layers-configuration-{spring-boot-xsd-version}.xsd">
 	<layers>
 		<layer>dependencies</layer>
 		<layer>snapshot-dependencies</layer>
@@ -554,7 +554,7 @@ This allows to reuse the cache for external dependencies when an internal depend
 	<layers-configuration xmlns="http://www.springframework.org/schema/boot/layers"
 						  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 						  xsi:schemaLocation="http://www.springframework.org/schema/boot/layers
-						  https://www.springframework.org/schema/boot/layers/layers-configuration.xsd">
+						  https://www.springframework.org/schema/boot/layers/layers-configuration-{spring-boot-xsd-version}.xsd">
 		<layers>
 			<layer>application</layer>
 			<layer>resources</layer>

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/projects/jar-layered-custom/jar/src/layers.xml

 <layers-configuration xmlns="http://www.springframework.org/schema/boot/layers"
 					  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 					  xsi:schemaLocation="http://www.springframework.org/schema/boot/layers
-					  https://www.springframework.org/schema/layers/layers-configuration.xsd">
+					  https://www.springframework.org/schema/layers/layers-configuration-2.3.xsd">
 	<layers>
 		<layer>configuration</layer>
 		<layer>application</layer>

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/test/resources/layers.xml

 <layers-configuration xmlns="http://www.springframework.org/schema/boot/layers"
 					  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 					  xsi:schemaLocation="http://www.springframework.org/schema/boot/layers
-					  https://www.springframework.org/schema/boot/layers/layers-configuration.xsd">
+					  https://www.springframework.org/schema/boot/layers/layers-configuration-2.3.xsd">
 	<layers>
 		<layer>configuration</layer>
 		<layer>application</layer>

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/test/resources/library-layer-no-filter.xml

 <layers-configuration xmlns="http://www.springframework.org/schema/boot/layers"
 					  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 					  xsi:schemaLocation="http://www.springframework.org/schema/boot/layers
-					  https://www.springframework.org/schema/boot/layers/layers-configuration.xsd">
+					  https://www.springframework.org/schema/boot/layers/layers-configuration-2.3.xsd">
 	<layers>
 		<layer>my-deps</layer>
 	</layers>

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/test/resources/resource-layer-no-filter.xml

 <layers-configuration xmlns="http://www.springframework.org/schema/boot/layers"
 					  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 					  xsi:schemaLocation="http://www.springframework.org/schema/boot/layers
-					  https://www.springframework.org/schema/boot/layers/layers-configuration.xsd">
+					  https://www.springframework.org/schema/boot/layers/layers-configuration-2.3.xsd">
 	<layers>
 		<layer>my-layer</layer>
 	</layers>