Fix AuthenticationSession field name in example

[mset]

The "Subject" field in AuthenticationSession is case-sensitive and thus needs to start with a capital in the config example.

Related issue(s)

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[aeneasr]

Thank you very much for your contribution to the documentation! Due to the way Docusaurus versioning works, you need to make the changes in two locations:

• docs/versioned_docs/version-v{version}/path/to/file
• docs/docs/path/to/file

Without making them in both locations, the changes will most likely be lost when releasing another version. Thank you! :)