feat(operator): set userAgent on Kubernetes client (kroxylicious#3624)

* Set userAgent on operator's Kubernetes client

Configure KUBERNETES_USER_AGENT env var in the operator Deployment
manifest using fabric8's built-in support. The value is interpolated
at build time via Maven resource filtering to include the project
version, e.g. "kroxylicious-operator/0.21.0".

Assisted-by: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Sam Barker <sam@quadrocket.co.uk>

* Add changelog entry for operator userAgent

Assisted-by: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Sam Barker <sam@quadrocket.co.uk>

---------

Signed-off-by: Sam Barker <sam@quadrocket.co.uk>

Author: SamBarker

CHANGELOG.md

@@ -7,6 +7,7 @@ Format `<github issue/pr number>: <short description>`.
 
 ## SNAPSHOT
 
+* [#3624](https://github.com/kroxylicious/kroxylicious/pull/3624): feat(operator): set Kubernetes client User-Agent to `kroxylicious-operator/<version>` for API server audit log identification
 * [#3565](https://github.com/kroxylicious/kroxylicious/pull/3514): build(deps): bump kubernetes-client.version from 7.5.2 to 7.6.1
 * [#3514](https://github.com/kroxylicious/kroxylicious/pull/3514): build(deps): build(deps-dev): bump org.yaml:snakeyaml from 2.5 to 2.6
 * [#3564](https://github.com/kroxylicious/kroxylicious/pull/3564): build(deps): bump apicurio-registry.version from 3.1.6 to 3.2.1

kroxylicious-operator/packaging/install/03.Deployment.kroxylicious-operator.yaml

@@ -39,6 +39,9 @@ spec:
               drop: ["ALL"]
             readOnlyRootFilesystem: true
           terminationMessagePolicy: FallbackToLogsOnError
+          env:
+            - name: KUBERNETES_USER_AGENT
+              value: "kroxylicious-operator/$[project.version]"
           args: [ ]
           resources:
             requests:

kroxylicious-operator/src/test/java/io/kroxylicious/kubernetes/operator/CreateKubernetesClientTest.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright Kroxylicious Authors.
+ *
+ * Licensed under the Apache Software License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
+ */
+
+package io.kroxylicious.kubernetes.operator;
+
+import org.junit.jupiter.api.Test;
+import org.junitpioneer.jupiter.SetEnvironmentVariable;
+
+import io.fabric8.kubernetes.client.KubernetesClientBuilder;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class CreateKubernetesClientTest {
+
+    @Test
+    @SetEnvironmentVariable(key = "KUBERNETES_USER_AGENT", value = "kroxylicious-operator/0.12.0")
+    void shouldUseUserAgentFromEnvironment() {
+        try (var client = new KubernetesClientBuilder().build()) {
+            assertThat(client.getConfiguration().getUserAgent())
+                    .isEqualTo("kroxylicious-operator/0.12.0");
+        }
+    }
+}