Add option to show recommeded fee on checkout invoice

Address #1036

BTCPayServer/Data/StoreBlob.cs

@@ -21,6 +21,7 @@ namespace BTCPayServer.Data
             MonitoringExpiration = 1440;
             PaymentTolerance = 0;
             RequiresRefundEmail = true;
+            ShowRecommendedFee = true;
         }
 
         [Obsolete("Use NetworkFeeMode instead")]
@@ -39,6 +40,8 @@ namespace BTCPayServer.Data
 
         public bool RequiresRefundEmail { get; set; }
 
+        public bool ShowRecommendedFee { get; set; }
+
         CurrencyPair[] _DefaultCurrencyPairs;
         [JsonProperty("defaultCurrencyPairs", ItemConverterType = typeof(CurrencyPairJsonConverter))]
         public CurrencyPair[] DefaultCurrencyPairs