refactor xmr rate module to exchange rate module for multi crypto support

backend/src/modules/exchangeRate/ExchangeRateModule.ts

@@ -0,0 +1,8 @@
+import { Module } from '@nestjs/common';
+import { ExchangeRateService } from './services/ExchangeRateService';
+
+@Module({
+    providers: [ExchangeRateService],
+    exports: [ExchangeRateService]
+})
+export class ExchangeRateModule {}