Document how to schedule driftctl on kubernetes

[sjourdan]

A commonly reported use case for driftctl is to schedule an hourly cron job in Kubernetes.
Let's give an example in the documentation!

Source k8s documentation: https://kubernetes.io/docs/tasks/job/automated-tasks-with-cron-jobs/

[sundowndev]

Started working on this at https://github.com/cloudskiff/helm but may be we should create a page in the docs about k8s without helm, then later create a chart when driftctl will become more stable. Also a chart would not be compatible with all k8s versions since CronJob definition became stable only at v1.20. Let me known what do you think about it!