Use dedicated k8s-migration-test-2204 agent label

Switch from the shared k8s-test-2204-8 pool to the dedicated
k8s-migration-test-2204 cloud (defined in
LiveRamp/kubernetes-deployments PR #6355) so the GCE->K8s migration
validation runs on an isolated EXCLUSIVE pool. Avoids interleaving
with unrelated org builds that default to k8s-common, which makes
failures attributable and prevents the test pool from being pinned
by long-running unrelated jobs.

Author: vemulaanvesh

Jenkinsfile

@@ -4,5 +4,5 @@
 env.JAVA_HOME = '/usr/lib/jvm/java-8-openjdk-amd64'
 
 mvnBuildPipeline {
-    agentLabel = 'k8s-test-2204-8'
+    agentLabel = 'k8s-migration-test-2204'
 }