[minor] Automated SaaS Job cleanup when auto_delete: false is set

[tomklapiscak]

Description

Adds the mas-saas-devops-job-cleaner script (and supporting mas.deploy.saas.jobcleaner library code for performing automated cleanup of orphaned Job resources when auto_delete: false is set in ArgoCD-managed MAS SaaS environments.

Job resources are routinely orphaned (i.e. marked for deletion by ArgoCD) since, when we need to apply an update to an immutable Job field (e.g. image tag), we must create a new version of the Job resource with a different name. When auto_delete: false is set, ArgoCD will (by design) not perform this cleanup for us. Over time, Job resources will accumulate and put pressure on the K8S API server.

The mas-saas-devops-job-cleaner script is run by a cluster-level CronJob defined in ibm-mas/gitops#257.

https://jsw.ibm.com/browse/MASCORE-5637

Testing

Refer to ibm-mas/gitops#257 for details of testing performed when this script is run via a CronJob in a MAS SaaS cluster.

Unit tests

Unit tests for the library code are included in this PR.