Slack integration for GHA failures (build cop)

[tyler-yankee]

Addresses #22019. Adds CI workflow for a custom Slack bot in DrakeDevelopers to send a notification to the #buildcop channel when GitHub Actions fails.

• The Slack workflow in CI is triggered when the main CI workflow finishes, and the "send notification" step happens when the main CI workflow failed (or timed out).
• The message is formatted as follows (save for the "test" names), with links to the failed run, the branch, and the repository:
• The Slack "app" (bot) that is running this, GitHub Actions Build Cop, is installed to the DrakeDevelopers workspace. I've added @jwnimmer-tri and @BetsyMcPhail as collaborators so that changes can be made as needed.

It turns out that GitHub's Slack integration doesn't support only filtering for workflow failures (see: integrations/slack#1563), which is why we're using the notify-slack-action instead.

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This change is 

[tyler-yankee]

I've tested the functionality on a dummy repository that you can see in the example above. Unfortunately, to do any further testing on drake-external-examples, the slack.yml file needs to be on main ... see https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#workflow_run.

[tyler-yankee]

Previously, tyler-yankee wrote…

I've tested the functionality on a dummy repository that you can see in the example above. Unfortunately, to do any further testing on drake-external-examples, the slack.yml file needs to be on main ... see https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#workflow_run.

+@BetsyMcPhail for feature review, please!

[BetsyMcPhail]

Reviewable status: 1 unresolved discussion, LGTM missing from assignee betsymcphail, LGTM missing from assignee nicolecheetham, platform LGTM missing (waiting on @nicolecheetham and @tyler-yankee)

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a discussion (no related file):

Previously, tyler-yankee (Tyler Yankee) wrote…

+@BetsyMcPhail for feature review, please!

+@nicolecheetham can you take over feature review on this please?

[nicolecheetham]

Overall looks good, mostly just a few tiny things here and there. Nice job!

Also, is there more work that needs to be done that hasn't been shown? Your last comment seems to suggest as such and I remember you mentioning needing to update the variable used for SLACK_WEBHOOK_URL.

Reviewable status: 7 unresolved discussions, LGTM missing from assignee nicolecheetham, platform LGTM missing (waiting on @tyler-yankee)

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.github/workflows/slack.yml line 11 at r1 (raw file):

jobs:
  notify:

nit consider renaming the job as to specify the type of notification. Maybe like notify_errors, failure_notifications, or error_notifications?

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.github/workflows/slack.yml line 14 at r1 (raw file):

    runs-on: ubuntu-latest
    steps:
      - name: Notify Build Cop Slack

nit similar to the job name.

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.github/workflows/slack.yml line 15 at r1 (raw file):

    steps:
      - name: Notify Build Cop Slack
        if: github.event.workflow_run.conclusion == 'failure' || github.event.workflow_run.conclusion == 'timed_out'

This expression should be surrounded by ${{ }}

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.github/workflows/slack.yml line 20 at r1 (raw file):

          status: ${{ github.event.workflow_run.conclusion }}
          notification_title: >
            ${{github.event.workflow_run.name}} failed on ${{github.event.workflow_run.head_branch}} -

nit I think you could replace "failed" with ${{github.event.workflow_run.conclusion}}. This would allow you to remove the message format line that says "Result: ..." simplifying the overall notification.

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.github/workflows/slack.yml line 21 at r1 (raw file):

          notification_title: >
            ${{github.event.workflow_run.name}} failed on ${{github.event.workflow_run.head_branch}} -
            <${{github.server_url}}/${{github.repository}}/actions/runs/${{github.event.workflow_run.id}}|View Failure>

nit The path can be simplified to ${{github.event.workflow_run.url}}

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.github/workflows/slack.yml line 25 at r1 (raw file):

            Result: ${{github.event.workflow_run.conclusion}}
            Run: ${{github.event.workflow_run.run_number}}
            Branch: <${{github.server_url}}/${{github.repository}}/tree/${{github.event.workflow_run.head_branch}}|${{github.repository}}/${{github.event.workflow_run.head_branch}}>

nit Is there a way to use ravsamhq/notify-slack-action@v2 customs variables to make the branch and footer notification less verbose code wise? Like {branch_url} and {repo_url}