Add Missing Enum to Freemium RMF Implementation (#1114)

**Required**:

Task/Issue URL:
https://app.asana.com/0/1206488453854252/1208904081551825/f
iOS PR: duckduckgo/iOS#3673
macOS PR: duckduckgo/macos-browser#3631
What kind of version bump will this require?: Patch

**Description**: Adding missing Freemium RMF enum

Sources/RemoteMessaging/Mappers/JsonToRemoteMessageModelMapper.swift

@@ -51,6 +51,7 @@ private enum AttributesKey: String, CaseIterable {
     case duckPlayerOnboarded
     case duckPlayerEnabled
     case messageShown
+    case isCurrentFreemiumPIRUser
 
     func matchingAttribute(jsonMatchingAttribute: AnyDecodable) -> MatchingAttribute {
         switch self {
@@ -86,6 +87,7 @@ private enum AttributesKey: String, CaseIterable {
         case .duckPlayerOnboarded: return DuckPlayerOnboardedMatchingAttribute(jsonMatchingAttribute: jsonMatchingAttribute)
         case .duckPlayerEnabled: return DuckPlayerEnabledMatchingAttribute(jsonMatchingAttribute: jsonMatchingAttribute)
         case .messageShown: return MessageShownMatchingAttribute(jsonMatchingAttribute: jsonMatchingAttribute)
+        case .isCurrentFreemiumPIRUser: return FreemiumPIRCurrentUserMatchingAttribute(jsonMatchingAttribute: jsonMatchingAttribute)
         }
     }
 }