Fix maven-jar-plugin version mismatch across modules

Root pluginManagement and netty-mqtt hardcoded version 3.1.1 while
the jar-plugin.version property (used by dao and others) was set to
3.4.0, causing build failures due to incompatible commons-io dependency.

Replace both hardcoded 3.1.1 occurrences with ${jar-plugin.version}
so all modules consistently use the version defined in one place.

Fixes #15037

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

netty-mqtt/pom.xml

@@ -125,7 +125,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-jar-plugin</artifactId>
-                <version>3.1.1</version>
+                <version>${jar-plugin.version}</version>
                 <configuration>
                     <archive>
                         <manifest>

pom.xml

@@ -635,7 +635,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-jar-plugin</artifactId>
-                    <version>3.1.1</version>
+                    <version>${jar-plugin.version}</version>
                 </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>