Proactively alert for long-running experiments without activity

[mikewilli]

I'm not sure if this is a reasonable task or what an implementation might look like, but it would be great if Experimenter could send alerts to a different/broader audience for potentially-abandoned experiments.

The context behind this is that there is a long-running experiment that Jetstream is continuing to faithfully analyze daily/weekly results for and the original experiment owner has left so no one ended the experiment.

┆Issue is synchronized with this Jira Task