Add enriched fields to channel member

PATCH {{_endpoint}}/services/data/v{{version}}/tooling/sobjects/PlatformEventChannelMember/:PLATFORM_EVENT_CHANNEL_MEMBER_ID

Request Body

{"FullName"=>"Account_Channel_chn_AccountChangeEvent", "Metadata"=>{"enrichedFields"=>[{"name"=>"External_Account_ID__c"}], "eventChannel"=>"Account_Channel__chn", "selectedEntity"=>"AccountChangeEvent"}}