[Doc] Automatic reload of certificates

[kaisecheng]

Release notes

[rn:skip]

What does this PR do?

Documents automatic TLS certificate reload behavior for Logstash.

Why is it important/What is the impact to the user?

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• Docs-only change
• Checked Markdown diff

How to test this PR locally

Related issues

• Relates Logstash automatic TLS Certificates reload #18892
• Closes Doc: add ssl.reload.automatic for pipeline tls reload #19031

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)
• run exhaustive tests : Run the exhaustive tests Buildkite pipeline.

[mergify]

This pull request does not have a backport label. Could you fix it @kaisecheng? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• If no backport is necessary, please add the backport-skip label

[github-actions]

Vale Linting Results

Summary: 3 suggestions found

💡 Suggestions (3)

File	Line	Rule	Message
docs/reference/logstash-settings-file.md	66	Elastic.WordChoice	Consider using 'can, might' instead of 'may', unless the term is in the UI.
docs/reference/logstash-settings-file.md	66	Elastic.Exclamation	Use exclamation points sparingly. Consider removing the exclamation point.
docs/reference/reloading-config.md	81	Elastic.WordChoice	Consider using 'efficiently' instead of 'simply', unless the term is in the UI.

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The Vale linter checks documentation changes against the Elastic Docs style guide.

To use Vale locally or report issues, refer to Elastic style guide for Vale.

[github-actions]

🔍 Preview links for changed docs

• docs/reference/logstash-settings-file.md
• docs/reference/reloading-config.md

[vishaangelova]

Thanks for this doc update!
We need to add an applies_to tag to clarify the version in which this configuration setting becomes available. Also this PR needs to be backported to the latest minor branch, as the docs are published from that branch.

[kaisecheng]

@vishaangelova thanks for reviewing this doc. The feature will be launched in 9.5.0. Currently, branch 9.5 doesn't exist yet, and it will be branched off main in the future. If I understand correctly, we don't need to backport this to 9.4 in order to publish the doc. Please correct me if I’m wrong.