Docs: Use sidecar pattern for Jenkins pod templates

User Story

As a developer using Jenkins to build my application
I want to use the base Jenkins agent image as a sidecar in my PodTemplate
So that I can use any s2i builder image in my Jenkins pipelines

Acceptance Criteria

• Provide new Kubernetes Plugin Pod Templates which uses the sidecar pattern for NodeJS and Maven.
• Add documentation on how to use the new pod template in a Jenkinsfile (need to specify the container where the build occurs).
• Add documentation on how developers can provide an inline pod template within a Jenkinsfile. Documentation should have the following formats:
  • New YAML declarative format
  • Deprecated Groovy format
• Existing pipelines that use the default Kubernetes Plugin Pod Templates do not break.
• End to end testing (for client or sync plugin) verifies that the new pod templates work.

QE Impact

QE will need to verify that the new pod templates can successfully execute a JenkinsPipeline build.

Docs Impact

Documentation needs to be updated to explain how to use the new template.

PX Impact

Unclear if we need new CEE/PX materials beyond doc updates.

Notes

We currently have built-in pod templates for NodeJS and Maven, which use specialized agent images with NodeJS/Maven image.
Blog post here outlines the process: https://developers.redhat.com/blog/2020/06/04/an-easier-way-to-create-custom-jenkins-containers/

The Groovy style of declaring in-line pod templates is deprecated in favor of a YAML-style format.

Existing documentation for the Jenkin pod templates: https://docs.openshift.com/container-platform/4.9/openshift_images/using_images/images-other-jenkins.html#images-other-jenkins-config-kubernetes_images-other-jenkins