Adapex: add Prebid.js bidder documentation

[floxis-admin]

Adds the bidder page for the Adapex Prebid.js adapter (biddercode: adapex), matching prebid/Prebid.js#15736.

• Banner, video and native; required seat and optional static floors. Floors guidance distinguishes intentional suppression/skips from unavailable floor data.
• Standard publisher FPD, EIDs, supply chain and PMP/deal ID handling; outstream requires a publisher-provided renderer.
• GVL ID 1609, storage disclosure and explicit storageAllowed opt-in for adpx_uid / user.ext.wlid; custom identity transmission additionally requires transmitEids and transmitUfpd. Denial removes supplied custom IDs and skips fallback storage/resolution.
• Iframe/pixel user sync on sync.adapex.io, with server-provided consent signals.
• Split-request telemetry identifies only the failed seat; ambiguous network failures without a response URL are omitted.
• Timeout/error telemetry is enabled by default, with a documented adapex.enableTelemetry: false opt-out. Beacons omit user, device and auction identifiers. Includes exported TypeScript parameter/configuration types.

Validation: repository-configured Markdown lint and bundle exec jekyll build pass at 886f3934. The rendered bidder page contains the updated publisher guidance.

Prebid Server support remains pbs: false. Its documentation will follow separately after the relevant server adapter has merged and been released.

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