Anonymised user ID module added

[kyrylenko]

Adds one page, dev-docs/modules/userid-submodules/anonymised.md. No other files change — the EID source and module name are carried in the page's front matter, which the userid layout renders into the User ID table.

The submodule reads an identifier that the Anonymised Marketing Tag has already stored in localStorage on the publisher's domain, and passes it to the bid stream as an EID under the source anonymised.io. It makes no network request and loads no script.

Beyond the standard configuration table and example, the page documents four things publishers get wrong otherwise:

• Do not configure storage. The Marketing Tag owns the identifier's lifecycle, including its removal on sign-out. A copy cached by Prebid.js would outlive that removal.
• Do not set userSync.ppid to anonymised.io. The Marketing Tag sets the Google Ad Manager PPID itself; letting Prebid.js set it too produces two different PPIDs for the same user, because Prebid strips non-alphanumeric characters from the ID first.
• Single-page applications should call pbjs.refreshUserIds({ submoduleNames: ['anonymisedId'] }) after a sign-in, and must pass submoduleNames so an unscoped refresh does not re-initialize every other ID submodule.
• localStorage is origin-scoped, so a publisher serving one user from several subdomains gets the identifier on each only once the tag has run there.

🏷 Type of documentation

• new feature

📋 Checklist

• Related pull requests in prebid.js or server are linked -> Anonymised id system module Prebid PR

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