document "scheduled_at" for the job api

3 jobs for bugs/#13461 in 18 minutes (queued for 2 seconds)
Status Name Job ID Coverage
  Lint
passed rubocop #1547658
grid5000-docker

00:01:32

 
  Test
passed test-for-buster #1547659
grid5000-docker

00:08:09

81.03%
 
  Deb
passed deb-for-buster #1547660
grid5000-docker

00:08:18