v11: Show user authentication data in the System Console user details page

[cwarnermm]

@claude Let's update the Mattermost Product Documentation to reflect the admin's user management product experience from Mattermost server v11 onward captured via mattermost/mattermost#33446

Starting from the master branch, ensure the docs PR is added to the v11-documentation branch. The doc updates focuses on the addition of Authentication Method to the user's information in the System Console which:
* Helps administrators troubleshoot authentication issues by showing external auth IDs
* Provides visibility into how users authenticate (LDAP DN, SAML NameID, OAuth ID, etc.)
* Makes it easier to correlate Mattermost users with their external authentication systems

[claude]

Claude finished @cwarnermm's task —— View job • claude/issue-8403-20250915-1920 • Create PR ➔

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Documentation updates for v11 Authentication Method feature completed! ✅

I've successfully updated the Mattermost Product Documentation to reflect the new Authentication Method field in System Console user details for v11.

Completed Tasks:

• Read repository guidelines (CLAUDE.md) - No CLAUDE.md found
• Explore documentation structure to find user management pages - Found main user management config page
• Review the referenced GitHub PR for implementation details - Used issue description details
• Update relevant documentation to include Authentication Method field
• Commit and push changes
• Provide PR creation link

What was updated:

Updated /source/administration-guide/configure/user-management-configuration-settings.rst to include:

• New Authentication Method field documentation under the "Review user data" section
• Explains how the field shows external authentication system details (LDAP DN, SAML NameID, OAuth ID, etc.)
• Describes how it helps system administrators troubleshoot authentication issues
• Notes how it enables easier correlation of Mattermost users with external authentication systems
• Specifies availability starting from Mattermost v11.0

The documentation update provides system administrators with clear information about this new feature that improves user management and authentication troubleshooting capabilities.

--- | Branch: claude/issue-8403-20250915-1920