chore(Jenkinsfile) switch to private registry and only build for arm64

- Use private registry: jenkins-infra/helpdesk#4769
- No need to build for `amd64` nowadays (less data to pull/push and less agents to use)

Author: dduportal

Jenkinsfile_k8s

@@ -1,4 +1,5 @@
 buildDockerAndPublishImage('jenkins-weeklyci', [
-    targetplatforms: 'linux/amd64,linux/arm64',
+    publishToPrivateAzureRegistry: true,
+    targetplatforms: 'linux/arm64',
     nextVersionCommand: 'echo "$(jx-release-version -next-version=semantic:strip-prerelease)-$(grep "FROM jenkins" Dockerfile | cut -d: -f2 | cut -d- -f1)"',
 ])