Dashboard: Add a Configuration Manager widget

Description of the need

The dashboard provides an overview of the status of the website. This overview does not include a widget with information about Configuration. This information and a link to the Configuration Manager would be very helpful.

Proposed solution

Let's add a Configuration Manager widget to the dashboard.

Alternatives that have been considered

I do not know if that has been discussed or proposed before, sorry!

Additional information

This could be a configurable block like the Available Updates block.

Draft of feature description for Press Release (1 paragraph at most)

Backdrop now includes a Configuration Manager widget on the Dashboard. This block shows you the status of your website's configuration, and provides a link to manage the Configuration Manager's Synchronize page.