Ensure java plugin is applied to avoid issues with using plugins{} syntax.

Author: srinivasankavitha

graphql-dgs-codegen-gradle/src/main/kotlin/com/netflix/graphql/dgs/codegen/gradle/CodegenPlugin.kt

@@ -20,9 +20,11 @@ package com.netflix.graphql.dgs.codegen.gradle
 
 import org.gradle.api.Plugin
 import org.gradle.api.Project
+import org.gradle.api.plugins.JavaPlugin
 import org.gradle.api.plugins.JavaPluginConvention
 import org.gradle.api.tasks.SourceSet
 
+
 @ExperimentalStdlibApi
 class CodegenPlugin : Plugin<Project> {
     override fun apply(project: Project) {
@@ -35,6 +37,8 @@ class CodegenPlugin : Plugin<Project> {
             it.dependsOn(taskProvider.get())
         }
 
+        project.plugins.apply(JavaPlugin::class.java)
+
         val javaConvention = project.convention.getPlugin(JavaPluginConvention::class.java)
         val sourceSets = javaConvention.sourceSets
         val mainSourceSet = sourceSets.getByName(SourceSet.MAIN_SOURCE_SET_NAME)