Monitor for core theme updates

[dsas]

We should have some alerting for core theme updates so that we can quickly apply those updates to dotcom. When we don't do this, users start getting concerned and asking questions. On atomic sites it shows that a theme update is available, but applying it won't work.

See PNEWy-cvG-p2 for how to perform the update

Before doing anything we should check whether this is necessary - if core themes are only updated with wp releases then we should already be well aware of the schedule.

[github-actions[bot]]

OpenAI suggested the following labels for this issue:

• [Feature Group] Appearance & Themes: The issue discusses updates related to core themes, which falls under the appearance and design aspects of WordPress sites.
• [Feature] .Org Themes: The issue specifically mentions core themes, which are often associated with themes imported from the WordPress.org repository.
• [Feature] Managed Plugins & Themes: The alert about managing core theme updates relates to how Automattic handles themes for Atomic sites.
• [Feature] Tracking Metrics & Monitoring: The suggestion to implement alerting for theme updates aligns with monitoring the system for timely actions.