Run updates with toolforge-jobs in Ansible deployment playbook

The periodic updates, when run on Grid Engine, were triggered via crontab (e2b2fccb),
which is now obsolete with the new Kubernetes-backed Toolforge-jobs framework.

The jobs can be loaded from a YAML file, so let's do that:

• Define the weekly-update job in Ansible variables
• Render it as YAML using the built-in copy module (which is not very recommended, but using template seems overkill)
• Notify handler to run toolforge jobs load

[1] https://wikitech.wikimedia.org/wiki/Help:Toolforge/Jobs_framework#Loading_jobs_from_a_YAML_file

Bug: T319813