[9.3] (backport #18860) Doc: Add page-level applies_to tags to Logstash content (Group 3)

[mergify]

Summary

Group 3: Monitoring, Management, and Operations (~23 files)
Adds applies_to tags to show applicability for each topic.

Related: https://github.com/elastic/docs-content-internal/issues/260

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
  Tool(s) and model(s) used: Cursor and claude-4.6-opus-high
• No

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This is an automatic backport of pull request #18860 done by [Mergify](https://mergify.com).

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🤖 GitHub comments

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Vale Linting Results

Summary: 2 suggestions found

💡 Suggestions (2)

File	Line	Rule	Message
docs/reference/monitoring-troubleshooting.md	15	Elastic.Versions	Use 'earlier versions' instead of 'older versions' when referring to versions.
docs/reference/monitoring-troubleshooting.md	15	Elastic.WordChoice	Consider using 'deactivated, deselected, hidden, turned off, unavailable' instead of 'disabled', unless the term is in the UI.

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[github-actions]

🔍 Preview links for changed docs

• docs/reference/configuring-centralized-pipelines.md
• docs/reference/configuring-geoip-database-management.md
• docs/reference/core-operations.md
• docs/reference/dashboard-monitoring-with-elastic-agent.md
• docs/reference/jvm-settings.md
• docs/reference/keystore.md
• docs/reference/logging.md
• docs/reference/logstash-centralized-pipeline-management.md
• docs/reference/logstash-geoip-database-management.md
• docs/reference/logstash-monitoring-ui.md

More links …

• docs/reference/logstash-pipeline-viewer.md
• docs/reference/logstash-settings-file.md
• docs/reference/managing-geoip-databases.md
• docs/reference/managing-logstash.md
• docs/reference/monitoring-internal-collection-legacy.md
• docs/reference/monitoring-logstash-legacy.md
• docs/reference/monitoring-logstash-with-elastic-agent.md
• docs/reference/monitoring-logstash.md
• docs/reference/monitoring-troubleshooting.md
• docs/reference/monitoring-with-elastic-agent.md
• docs/reference/monitoring-with-metricbeat.md
• docs/reference/secure-connection.md
• docs/reference/serverless-monitoring-with-elastic-agent.md