GumGum: Enable Opt-In change notification for GumGum Adapter (prebid#4006)

Author: sindhuja-sridharan

.github/workflows/scripts/codepath-notification

@@ -22,3 +22,4 @@ pubmatic|Pubmatic: header-bidding@pubmatic.com
 openx|OpenX: prebid@openx.com
 medianet|Medianet: prebid@media.net
 thetradedesk|TheTradeDesk: Prebid-Maintainers@thetradedesk.com
+gumgum|GumGum: prebid@gumgum.com