Enable metadata repository

[melix]

Issue description

In order to let us move to the metadata repository, the Micronaut Gradle plugin needs to enable the metadata repository by default.

This can be done with this patch:

diff --git a/graalvm-plugin/src/main/java/io/micronaut/gradle/graalvm/MicronautGraalPlugin.java b/graalvm-plugin/src/main/java/io/micronaut/gradle/graalvm/MicronautGraalPlugin.java
index 4a8c8c0..42c14ea 100644
--- a/graalvm-plugin/src/main/java/io/micronaut/gradle/graalvm/MicronautGraalPlugin.java
+++ b/graalvm-plugin/src/main/java/io/micronaut/gradle/graalvm/MicronautGraalPlugin.java
@@ -5,11 +5,13 @@ import io.micronaut.gradle.MicronautRuntime;
 import io.micronaut.gradle.PluginsHelper;
 import org.graalvm.buildtools.gradle.NativeImagePlugin;
 import org.graalvm.buildtools.gradle.dsl.GraalVMExtension;
+import org.graalvm.buildtools.gradle.dsl.GraalVMReachabilityMetadataRepositoryExtension;
 import org.graalvm.buildtools.gradle.tasks.BuildNativeImageTask;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.DependencySet;
 import org.gradle.api.file.RegularFile;
+import org.gradle.api.plugins.ExtensionAware;
 import org.gradle.api.plugins.JavaPluginConvention;
 import org.gradle.api.provider.ListProperty;
 import org.gradle.api.provider.Provider;
@@ -62,6 +64,8 @@ public class MicronautGraalPlugin implements Plugin<Project> {
             configureAnnotationProcessing(project, extension);
         });
         GraalVMExtension graal = project.getExtensions().findByType(GraalVMExtension.class);
+        GraalVMReachabilityMetadataRepositoryExtension metadataRepositoryExtension = ((ExtensionAware) graal).getExtensions().findByType(GraalVMReachabilityMetadataRepositoryExtension.class);
+        metadataRepositoryExtension.getEnabled().convention(true);
         graal.getBinaries().configureEach(options ->
                 {
                     options.resources(rsrc -> rsrc.autodetection(inf -> {

I have tentatively put the milestone for 4.0.0 which would mean Micronaut 4, but we can do it earlier if we want to, it depends on when we are ready to move.