CF-934: Add support for a custom Fiat exchange rate provider (#1110)

Author: thoagb

server_extensions_api/src/main/java/com/generalbytes/batm/server/extensions/IExtension.java

@@ -224,4 +224,14 @@ default Set<ITravelRuleProviderFactory> getTravelRuleProviderFactories() {
      */
     Set<IWalletTypeEvaluationProvider> getWalletTypeEvaluationProviders();
 
+    /**
+     * Get fiat exchange rate providers.
+     *
+     * @return Set of fiat exchange rate providers.
+     * @see IFiatExchangeRateProvider
+     */
+    default Set<IFiatExchangeRateProvider> getFiatExchangeRateProviders() {
+        return Collections.emptySet();
+    }
+
 }

server_extensions_api/src/main/java/com/generalbytes/batm/server/extensions/IFiatExchangeRateProvider.java

@@ -23,7 +23,19 @@
 
 public interface IFiatExchangeRateProvider {
     public Set<String> getFiatCurrenciesFrom();
+
     public Set<String> getFiatCurrenciesTo();
 
     public BigDecimal getRate(String fromCurrency, String toCurrency);
+
+    /**
+     * Determines the priority of this exchange rate provider in relation to other providers.
+     * Higher weight value indicates higher priority when multiple providers are available.
+     * Built-in providers have a weight value of {@code 0}.
+     *
+     * @return Weight value indicating the provider's priority. Returns {@code 0} if no specific priority is set.
+     */
+    default int getPriorityWeight() {
+        return 0;
+    }
 }