Bryce/add monitor troubleshooting section

[buraizu]

What does this PR do?

Adds a guide for troubleshooting monitor alerts.

Motivation

DOCS-3650

Preview

https://docs-staging.datadoghq.com/bryce/add-monitor-troubleshooting-section/monitors/guide/troubleshooting-monitor-alerts/

Additional Notes

---

Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/bryce/add-monitor-troubleshooting-section/monitors/guide/troubleshooting-monitor-alerts

Modified Files

• https://docs-staging.datadoghq.com/bryce/add-monitor-troubleshooting-section/monitors/guide/

[urseberry]

Editorial review on DOCS-4033

[buraizu]

@urseberry Thank you for that feedback!