Use ROOT component name

docs/antora.yml

@@ -1,4 +1,4 @@
-name: ''
+name: ROOT
 title: Spring Security
 version: 5.6
 start_page: ROOT:index.adoc

docs/spring-security-docs.gradle

@@ -24,7 +24,7 @@ tasks.register("generateAntora") {
 		def outputFile = new File("$buildDir/generateAntora/antora.yml")
 		outputFile.getParentFile().mkdirs()
 		outputFile.createNewFile()
-		outputFile.setText("""name: ''
+		outputFile.setText("""name: ROOT
 title: Spring Security
 version: 5.6
 start_page: ROOT:index.adoc