fixes frontmatter entries for a few content files

[StefonSimmons]

What does this PR do? What is the motivation?

Fixes frontmatter errors (duplicate and null entries) similar to https://github.com/DataDog/websites-modules/pull/542

• running hugo build --templateMetrics for Docs throws an error on these files

preview: https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys

Merge readiness

• Ready for merge

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Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys/actions/app_builder/queries
• https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys/agent/guide/agent-5-autodiscovery
• https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys/agent/guide/agent-5-kubernetes-basic-agent-usage
• https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys/error_tracking/frontend/mobile/unity
• https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys/observability_pipelines/legacy/
• https://docs-staging.datadoghq.com/stefon.simmons/rm-dupe-keys/real_user_monitoring/error_tracking/mobile/unity