CI(label-for-external-users): add retry logic for unexpected errors

[bayandin]

Problem

One of the PRs[1] opened by a neondatabase org member got labelled as external because the gh api call failed in the wrong way[2]:

Get "https://api.github.com/orgs/neondatabase/members/cloneable": dial tcp 140.82.114.5:443: i/o timeout
is-member=false

• [1] proxy: don't let one timeout eat entire retry budget #8924
• [2] https://github.com/neondatabase/neon/actions/runs/10718126837/job/29719341618

Summary of changes

• Check that the error message is expected before labelling PRs
• Retry gh api call for 10 times in case of unexpected error messages
• Add workflow_dispatch trigger

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3829 tests run: 3719 passed, 0 failed, 110 skipped (full report)

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Flaky tests (2)

Postgres 16

• test_location_conf_churn[2]: release-x86-64
• test_subscriber_restart: release-x86-64

Code coverage* (full report)

• functions: 31.9% (7390 of 23138 functions)
• lines: 50.3% (59657 of 118607 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
05a6157 at 2024-09-05T18:23:21.601Z :recycle:}

[koivunej]

I am not entirely sure if we need the retry loop, but you've already implemented it so lets enjoy it. I guess this will help to better debug any unexpected stuff as well.