[dagit] Show start/end information on latest run in Job details
On the job details header metadata, add a tooltip to the duration text to indicate the started/ended values of the run.
I don't really have enough space here to add these directly to the header instead of the duration, but hopefully this is useful.
Test Plan: View a job with a run, verify that the tooltip shows the correct information.
Reviewers: bengotow, sandyryza
Reviewed By: sandyryza
Differential Revision: https://dagster.phacility.com/D8956