Export grace time as a metric so that it can be used in dashboards

[mem]

From the comment in the code review:

          This will have to wait for another time, but you can create a metric with that information (grace time), and you can use that metric in a dashboard to show where the indicator is crossing that value instead of refering to a particular line in the source code.

Originally posted by @mem in https://github.com/grafana/deployment_tools/pull/182269#discussion_r1834369200