chore(ci): send alert message when stencil-nightly workflow finishes (#30743)

Send alert to a Discord channel using a webhook.

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## What is the current behavior?
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## What is the new behavior?
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- If a step in the workflow fails, an alert message will be sent to a
Discord channel using a webhook.

## Does this introduce a breaking change?

- [ ] Yes
- [X] No

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## Other information

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Co-authored-by: Brandy Smith <brandyscarney@users.noreply.github.com>