[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	77	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