Make archetype an extension instead of a plug-in per various web
comments:
  https://github.com/oracle/helidon/issues/1025
Issue-ID: POLICY-3126
Change-Id: I6703d832065d3b08fbc3c6613e049c30d2ee2c50
Signed-off-by: Jim Hahn <jrh3@att.com>
     </scm>
 
     <build>
+        <extensions>
+            <extension>
+                <groupId>org.apache.maven.archetype</groupId>
+                <artifactId>archetype-packaging</artifactId>
+                <version>3.2.0</version>
+            </extension>
+        </extensions>
         <pluginManagement>
             <plugins>
                 <plugin>
                     <artifactId>maven-archetype-plugin</artifactId>
                     <version>3.2.0</version>
                 </plugin>
-                <plugin>
-                    <groupId>org.apache.maven.archetype</groupId>
-                    <artifactId>archetype-packaging</artifactId>
-                    <version>3.2.0</version>
-                </plugin>
                 <plugin>
                     <groupId>com.coderplus.maven.plugins</groupId>
                     <artifactId>copy-rename-maven-plugin</artifactId>