docs: Document AGENT_CONTROL_RUNTIME_TOKEN_HEADER

[sheilattran8]

Describe your changes

Added AGENT_CONTROL_RUNTIME_TOKEN_HEADER to the Configuration page.

Jira ticket

https://splunk.atlassian.net/browse/O11YDOCS-8543

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• - Is this ready for review? If not, raise as a draft PR
• - This deployed to a staging environment correctly
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• - I have tested any code that is added or updated
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• - I have verified all images and videos match production (or dev for unreleased features)
• - I have tested that the content matches the functionality in production (or dev for unreleased features)
• - All checks have passed
• - This references a feature that is public. If not, add a note and we can schedule the merge for after the feature release

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Project	Status	Preview	Updated (UTC)
agentcontrol	🟢 Ready	View Preview	Aug 25, 2026, 5:02 PM

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