AcuityAds Bid Adapter: add gpp support (prebid#4896)

* add prebid.js adapter

* updates

* updates

* update Prebid Server documentation

* add gpp

Author: AcuityAdsIntegrations

dev-docs/bidders/acuityads.md

@@ -9,6 +9,7 @@ tcfeu_supported: true
 usp_supported: true
 coppa_supported: true
 schain_supported: true
+gpp_supported: true
 userId: britepoolId, criteo, id5Id, identityLink, liveIntentId, netId, parrableId, pubCommonId, unifiedId
 media_types: banner, video, native
 safeframes_ok: true