Show prepare breeze timing in CI duration alerts

[gopidesupavan]

CI duration alerts currently identify slower jobs but do not surface whether
the setup phase accounts for the change. Showing the prepare breeze step timing
makes common CI image/cache slowdowns visible without adding noisy per-step
analysis for every job.

The first job spent most of its extra time preparing the image, and in some cases that includes downloading the stash. Adding the Prepare breeze & CI image timing makes that setup cost visible directly in the duration alert.

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[gopidesupavan]

it produces now something like this:

[github-actions]

Backport successfully created: v3-3-test

Note: As of Merging PRs targeted for Airflow 3.X
the committer who merges the PR is responsible for backporting the PRs that are bug fixes (generally speaking) to the maintenance branches.

In matter of doubt please ask in #release-management Slack channel.

Status	Branch	Result
✅	v3-3-test

[potiuk]

Let's see - sometimes that duration will be longer - mostly when we need to rebuild the image. I think we should simply exclude the image build time and track it separately.,