Run import job as Kubernetes CronJob

[Mr0grog]

Instead of running the import job as a cron script on a random EC2 VM, run it as an actual CronJob in Kubernetes with everything else. This also cleans up the docs around jobs.

Why do this now? See:

• https://github.com/edgi-govdata-archiving/web-monitoring/issues/168
• https://github.com/edgi-govdata-archiving/web-monitoring-processing/issues/757

Work not visible here:

• Created a new IAM account for jobs that can write to relevant S3 buckets.
• Added ability to store cache files in S3 (https://github.com/edgi-govdata-archiving/web-monitoring-processing/pull/849) since we have no persistent storage in Kubernetes.