Improve example group timing information

Context

Follow-up of gitlab-org/quality/engineering-productivity/team#323 (comment 1681695489)

What does this MR do and why?

• Add spec file to example group duration message (so that we can search for it in the expected list quickly from the job output)
• Display expected duration at the start of the RSpec job (we cannot download the artifacts when the job timed out)

Proof of work

See https://gitlab.com/gitlab-org/gitlab/-/jobs/5694899496 as an example:

# Example group Ci::Pipeline (./spec/models/ci/pipeline_spec.rb) took 4 minutes 1.25 seconds.
# RSpec elapsed time: 4 minutes 4.68 seconds.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.