Make 'generateGradleOptions' task visible

Makes all generate* tasks easier to discover.

^KT-27301 In Progress

buildSrc/src/main/kotlin/CommonUtil.kt

@@ -55,6 +55,7 @@ var Project.javaHome: String?
     }
 
 fun Project.generator(fqName: String, sourceSet: SourceSet? = null, configure: JavaExec.() -> Unit = {}) = smartJavaExec {
+    group = "Generate"
     classpath = (sourceSet ?: testSourceSet).runtimeClasspath
     mainClass.set(fqName)
     workingDir = rootDir