Document job/pipeline retry

Context

https://gitlab.com/gitlab-org/gitlab/-/issues/508338#note_2251465006

Problem

Job retry is mentioned in several docs but there is no SSoT in the user docs about what it means retrying a job or pipeline. Users may not be aware of the side-effects of retrying a job.

Proposal

Have a section in https://docs.gitlab.com/ee/ci/jobs that describes the retry functionality covering:

• When a job is retried, a clone of the job is created and executed instead. User is redirected to a different page with a new job ID.
  • Previous failing jobs that have been retried are still persisted but hidden from the pipeline view.
• When a job is retried, the new job running will be associated to the user that initiated the retry.
• When a job is retried, any subsequent jobs that were skipped (due to a job failure) are reassigned to the user that initiated the retry.

In addition we should describe:

• pipeline retry is a bulk retry of all the failed jobs, with the same side-effects as above.
• retrying a bridge/trigger job carries the same side-effects as above.