ZIP publication groupId value is configurable (#4156)

When publishing Zip POM the groupId value was hard-coded to `org.opensearch.plugin` value which worked fine for existing core plugins but is not convenient for other plugins (such as community plugins maintained in independent repositories).

This PR changes the sources of the ZIP publishing groupId value.

Specifically, there are two ways to set the value:
1) It is automatically inherited from the Gradle "project.group"
2) It can be manually specified in the ZIP publication POM object

This PR also brings a major rework of tests in PublishTests class. Individual testing scenarios are driven by "real" gradle building scripts (utilizing `java-gradle-plugin` gradle plugin).

Closes #3692

Signed-off-by: Lukáš Vlček <lukas.vlcek@aiven.io>

Signed-off-by: Lukáš Vlček <lukas.vlcek@aiven.io>

CHANGELOG.md

@@ -8,6 +8,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Changed
 - Dependency updates (httpcore, mockito, slf4j, httpasyncclient, commons-codec) ([#4308](https://github.com/opensearch-project/OpenSearch/pull/4308))
 - Use RemoteSegmentStoreDirectory instead of RemoteDirectory ([#4240](https://github.com/opensearch-project/OpenSearch/pull/4240))
+- Plugin ZIP publication groupId value is configurable ([#4156](https://github.com/opensearch-project/OpenSearch/pull/4156))
 
 ### Deprecated
 

buildSrc/src/main/java/org/opensearch/gradle/pluginzip/Publish.java

@@ -9,7 +9,8 @@
 
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
-import org.gradle.api.publish.Publication;
+import org.gradle.api.logging.Logger;
+import org.gradle.api.logging.Logging;
 import org.gradle.api.publish.PublishingExtension;
 import org.gradle.api.publish.maven.MavenPublication;
 import org.gradle.api.publish.maven.plugins.MavenPublishPlugin;
@@ -18,6 +19,9 @@
 import org.gradle.api.Task;
 
 public class Publish implements Plugin<Project> {
+
+    private static final Logger LOGGER = Logging.getLogger(Publish.class);
+
     public final static String EXTENSION_NAME = "zipmavensettings";
     public final static String PUBLICATION_NAME = "pluginZip";
     public final static String STAGING_REPO = "zipStaging";
@@ -37,27 +41,25 @@ public static void configMaven(Project project) {
                 });
             });
             publishing.publications(publications -> {
-                final Publication publication = publications.findByName(PUBLICATION_NAME);
-                if (publication == null) {
-                    publications.create(PUBLICATION_NAME, MavenPublication.class, mavenZip -> {
-                        String zipGroup = "org.opensearch.plugin";
-                        String zipArtifact = project.getName();
-                        String zipVersion = getProperty("version", project);
-                        mavenZip.artifact(project.getTasks().named("bundlePlugin"));
-                        mavenZip.setGroupId(zipGroup);
-                        mavenZip.setArtifactId(zipArtifact);
-                        mavenZip.setVersion(zipVersion);
-                    });
-                } else {
-                    final MavenPublication mavenZip = (MavenPublication) publication;
-                    String zipGroup = "org.opensearch.plugin";
-                    String zipArtifact = project.getName();
-                    String zipVersion = getProperty("version", project);
-                    mavenZip.artifact(project.getTasks().named("bundlePlugin"));
-                    mavenZip.setGroupId(zipGroup);
-                    mavenZip.setArtifactId(zipArtifact);
-                    mavenZip.setVersion(zipVersion);
+                MavenPublication mavenZip = (MavenPublication) publications.findByName(PUBLICATION_NAME);
+
+                if (mavenZip == null) {
+                    mavenZip = publications.create(PUBLICATION_NAME, MavenPublication.class);
                 }
+
+                String groupId = mavenZip.getGroupId();
+                if (groupId == null) {
+                    // The groupId is not customized thus we get the value from "project.group".
+                    // See https://docs.gradle.org/current/userguide/publishing_maven.html#sec:identity_values_in_the_generated_pom
+                    groupId = getProperty("group", project);
+                }
+
+                String artifactId = project.getName();
+                String pluginVersion = getProperty("version", project);
+                mavenZip.artifact(project.getTasks().named("bundlePlugin"));
+                mavenZip.setGroupId(groupId);
+                mavenZip.setArtifactId(artifactId);
+                mavenZip.setVersion(pluginVersion);
             });
         });
     }