Adnuntius Bid Adaptor: add new advertiserTransparency feature

[antosarho]

Adds documentation for the new advertiserTransparency feature.

🏷 Type of documentation

• [x] new feature

📋 Checklist

• [x] Related pull requests in prebid.js or server are linked -> https://github.com/prebid/Prebid.js/pull/11866

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