How to document privacy sandbox support by bidders

[muuki88]

Google is moving forward with the privacy sandbox implementations and more and more bidders are starting to support PAPPI (fka Fledge).

In this PR #4955 there was the first request to document support on a bidder page.

Open questions

1. Should we document this at all?
2. How should we document it? A new filed for PAPPI only, or "sandbox features" with PAPPI, topics and what might yet to come

[muuki88]

• PAAPI support is relevant
• Attestation files available

Publisher PMC will provide a set of requirements.

[muuki88]

Unruly now has documented fledge support, too #4977

[muuki88]

Proposal.

New filed privacy_sandbox with allowed values paapi and topics

[muuki88]

https://github.com/prebid/Prebid.js/pull/10755 adding pappi support