payloadLifespan/payloadLifetime and other name variants unified to Time To Live naming.

code/MessengerApi/Handlers/Endpoint/SendEndpointHandler.cs

@@ -32,7 +32,7 @@ namespace MessengerApi.Handlers.Endpoint
             Guid? toUserId,
             string payload,
             string payloadType,
-            int? payloadLifespanInSeconds)
+            int? timeToLiveInSeconds)
         {
             // Authorize.
             var targetRecipientId = toUserId.HasValue
@@ -50,7 +50,7 @@ namespace MessengerApi.Handlers.Endpoint
                 ToId = targetRecipientId,
                 Payload = payload,
                 PayloadType = payloadType,
-                PayloadLifespanInSeconds = payloadLifespanInSeconds ?? (this.configuration.DefaultMessageLifetimeInMinutes * 60)
+                TimeToLiveInSeconds = timeToLiveInSeconds ?? (this.configuration.DefaultMessageTimeToLiveInSeconds)
             };
 
             this.unitOfWork.Messages.Add(message);