KAFKA-7047: Added SimpleHeaderConverter to plugin isolation whitelist

This was originally missed when headers were added as part of KIP-145 in AK 1.1. An additional unit test was added in line with the StringConverter.

This should be backported to the AK `1.1` branch so that it is included in the next bugfix release. The `SimpleHeaderConverter` class that we're referencing was first added in the 1.1.0 release, so there's no reason to backport earlier.

Author: Randall Hauch <rhauch@gmail.com>

Reviewers: Ewen Cheslack-Postava <ewen@confluent.io>

Closes #5204 from rhauch/kafka-7047

connect/runtime/src/main/java/org/apache/kafka/connect/runtime/isolation/PluginUtils.java

@@ -128,6 +128,7 @@ public class PluginUtils {
             + "|file\\..*"
             + "|converters\\..*"
             + "|storage\\.StringConverter"
+            + "|storage\\.SimpleHeaderConverter"
             + "|rest\\.basic\\.auth\\.extension\\.BasicAuthSecurityRestExtension"
             + ")"
             + "|common\\.config\\.provider\\.(?!ConfigProvider$).*"

connect/runtime/src/test/java/org/apache/kafka/connect/runtime/isolation/PluginUtilsTest.java

@@ -164,6 +164,9 @@ public class PluginUtilsTest {
         assertTrue(PluginUtils.shouldLoadInIsolation(
                 "org.apache.kafka.connect.storage.StringConverter")
         );
+        assertTrue(PluginUtils.shouldLoadInIsolation(
+                "org.apache.kafka.connect.storage.SimpleHeaderConverter")
+        );
         assertTrue(PluginUtils.shouldLoadInIsolation(
             "org.apache.kafka.connect.rest.basic.auth.extension.BasicAuthSecurityRestExtension"
         ));