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

backend/src/modules/exchangeRate/const/coingeckoIds.ts

@@ -0,0 +1,7 @@
+import type { ExchangeRatePaymentMethod } from './exchangeRatePaymentMethods';
+import { PaymentMethod } from '../../payment/types/PaymentMethod';
+
+export const COINGECKO_ID_BY_PAYMENT_METHOD = {
+    [PaymentMethod.Xmr]: 'monero',
+    [PaymentMethod.Btc]: 'bitcoin'
+} as const satisfies Record<ExchangeRatePaymentMethod, string>;