chore(android): create an ApiManager class

android/app/src/main/java/com/vernu/sms/ApiManager.java

@@ -0,0 +1,33 @@
+package com.vernu.sms;
+
+import com.vernu.sms.services.GatewayApiService;
+
+import retrofit2.Retrofit;
+import retrofit2.converter.gson.GsonConverterFactory;
+
+public class ApiManager {
+    private static GatewayApiService apiService;
+
+    public static GatewayApiService getApiService() {
+        if (apiService == null) {
+            apiService = createApiService();
+        }
+        return apiService;
+    }
+
+    private static GatewayApiService createApiService() {
+//        OkHttpClient.Builder httpClient = new OkHttpClient.Builder();
+//        HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor();
+//        loggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
+//        httpClient.addInterceptor(loggingInterceptor);
+
+        Retrofit retrofit = new Retrofit.Builder()
+                .baseUrl(AppConstants.API_BASE_URL)
+//                .client(httpClient.build())
+                .addConverterFactory(GsonConverterFactory.create())
+                .build();
+        apiService = retrofit.create(GatewayApiService.class);
+
+        return retrofit.create(GatewayApiService.class);
+    }
+}