clarify what is a running workspace

[akosyakov]

Some users are confused by the dashboard showing the total workspace time (current - creation) as running and get worried that they are charged while images built, pulled and so on: gitpod-io/gitpod#3042 (comment)

I could not find a clear definition of Gitpod hours in regard to the workspace lifecycle here: https://www.gitpod.io/docs/subscriptions/

Maybe we should also reconsider what time we display on the dashboard. cc @gtsiolis