Improve explanation of dsl names in config docs

[fearful-symmetry]

Proposed commit message

closes #36733

This expands the config documentation for DSL, elaborating on the template variables used by the data_stream_pattern config value.

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
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

[fearful-symmetry]

heartbeat CI error seems unrelated...

[elasticmachine]

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• Start Time: 2023-10-04T20:08:38.743+0000

• Duration: 99 min 22 sec

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Test	Results
Failed	0
Passed	28478
Skipped	2013
Total	30491

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[vigneshshanmugam]

HB changes LGTM

[bhapas]

LGTM

[fearful-symmetry]

@Mergifyio backport 8.11

[mergify]

backport 8.11

✅ Backports have been created

• #36766 [8.11](backport #36750) Improve explanation of dsl names in config docs has been created for branch 8.11