Enable Slack notifications on pipeline start for megatests

[maxulysse]

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.06%. Comparing base (f82c4dc) to head (70e18d2).

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mashehu]

how does this work, will it update the same message or post one for start, one for a finished run?

[maxulysse]

how does this work, will it update the same message or post one for start, one for a finished run?

That should display a link to the run when failing, according to @adamrtalbot who is working on a release to make sure it works on success too.

cf https://nfcore.slack.com/archives/C03MDE53ZCP/p1782377748129469?thread_ts=1782376428.099719&cid=C03MDE53ZCP

[mashehu]

looking at the documentation, it looks like it will be two messages then. given that we usually run at least three times, this gets quite spammy.
@adamrtalbot how difficult is it to just have one message per run, that gets updated in place based on the status, e.g. first has running and then success.