Include the current timestamp in the Thanos overview URL

What does this MR do?

We include a link to a Thanos query to show the health status with each production health check message. However, these links aren't meaningful for historical information because the URL as written would always load the current state of the system, not the state as it was when the message was posted.

Now we include the timestamp at the time of generating the message.

This also removes extraneous arguments from the query string.