Restore checkstyle

Rather than disabling checkstyle altogether, this commit enables it
again, relaxing the javadoc requirement only.

See gh-7142

spring-boot-docs/pom.xml

@@ -17,7 +17,6 @@
 	</organization>
 	<properties>
 		<main.basedir>${basedir}/..</main.basedir>
-		<disable.checks>true</disable.checks>
 	</properties>
 	<dependencies>
 		<dependency>

spring-boot-parent/src/checkstyle/checkstyle-suppressions.xml

@@ -13,6 +13,7 @@
 	<suppress files="[\\/]src[\\/]test[\\/]java[\\/]" checks="Javadoc*" />
 	<suppress files="[\\/]autoconfigure[\\/]" checks="JavadocType" />
 	<suppress files="[\\/]autoconfigure[\\/]" checks="JavadocVariable" />
+	<suppress files="[\\/]spring-boot-docs[\\/]" checks="JavadocType" />
 	<suppress files="[\\/]spring-boot-samples[\\/]" checks="JavadocType" />
 	<suppress files="[\\/]spring-boot-deployment-tests[\\/]" checks="JavadocType" />
 	<suppress files="[\\/]spring-boot-integration-tests[\\/]" checks="JavadocType" />