Add sats as a native currency

This will allow you to create an invoice where its primary currency is denominated in sats

BTCPayServer.Common/Altcoins/BTCPayNetworkProvider.Bitcoin.cs

@@ -21,6 +21,11 @@ namespace BTCPayServer
                 UriScheme = "bitcoin",
                 CryptoImagePath = "imlegacy/bitcoin.svg",
                 LightningImagePath = "imlegacy/bitcoin-lightning.svg",
+                DefaultRateRules = new[]
+                {
+                    "SATS_X = SATS_BTC * BTC_X",
+                    "BTC_SATS = sats(BTC_SATS);",
+                },
                 DefaultSettings = BTCPayDefaultSettings.GetDefaultSettings(NetworkType),
                 CoinType = NetworkType == NetworkType.Mainnet ? new KeyPath("0'") : new KeyPath("1'"),
                 SupportRBF = true,

BTCPayServer/Payments/Lightning/LightningLikePaymentHandler.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;

BTCPayServer/Services/Rates/CurrencyNameTable.cs

@@ -98,6 +98,12 @@ namespace BTCPayServer.Services.Rates
                     {
                         AddCurrency(_CurrencyProviders, network.CryptoCode, 8, network.CryptoCode);
                     }
+
+                    _CurrencyProviders.TryAdd("SATS",
+                        new NumberFormatInfo()
+                        {
+                            CurrencySymbol = "sats", CurrencyDecimalDigits = 0, CurrencyPositivePattern = 3
+                        });
                 }
                 return _CurrencyProviders.TryGet(currency.ToUpperInvariant());
             }
@@ -189,6 +195,15 @@ namespace BTCPayServer.Services.Rates
                 }
             }
 
+            dico.TryAdd("SATS", new CurrencyData()
+            {
+                Code = "SATS",
+                Crypto = true,
+                Divisibility = 0,
+                Name = "Satoshis",
+                Symbol = "Sats",
+            });
+
             return dico.Values.ToArray();
         }