Add Netty BOM to dependency management to resolve version conflicts

AsyncHttpClient 3.0.3 brings in various Netty 4.2 modules transitively,
but the project also has old Netty 4.0.x versions defined (netty.version
and netty.all.version). This version mismatch was causing runtime failures
where no HTTP requests were being sent.

By adding the Netty BOM (Bill of Materials) to dependencyManagement, all
Netty modules across the project will be forced to use version 4.2.7.Final
consistently, preventing classpath conflicts.

This should resolve the test failures in KairosDbSinkTest where requests
were not being sent to the mock server.

Author: claude

pom.xml

@@ -976,6 +976,13 @@
         <scope>import</scope>
         <type>pom</type>
       </dependency>
+      <dependency>
+        <groupId>io.netty</groupId>
+        <artifactId>netty-bom</artifactId>
+        <version>${netty.codec.http.version}</version>
+        <scope>import</scope>
+        <type>pom</type>
+      </dependency>
     </dependencies>
   </dependencyManagement>
   <profiles>