added functionality to spoonacular lib to convert units

backend/src/main/spoonaccular/AmountConversion.java

@@ -0,0 +1,34 @@
+package spoonaccular;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.cdimascio.dotenv.Dotenv;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.Response;
+import spoonaccular.models.amount_conversion.ConvertedAmount;
+
+import java.io.IOException;
+
+public class AmountConversion {
+
+    private static final OkHttpClient client =  new OkHttpClient();
+    private static final Dotenv dotenv = Dotenv.configure().ignoreIfMissing().ignoreIfMalformed().load();
+
+    private AmountConversion(){
+    }
+
+    public static double convertAmount(String ingrdientName, Double sourceAmount, String sourceUnit, String targetUnit) throws IOException {
+        Request request = APIAuthentication.addAuthHeaders(
+                new Request.Builder()
+                        .url("https://" + dotenv.get("X-RapidAPI-Host") +
+                        "recipes/convert?ingredientName=" + ingrdientName +
+                        "&targetUnit=" + targetUnit +
+                        "&sourceUnit=" + sourceUnit +
+                        "&sourceAmount=" + sourceAmount)
+        ).build();
+        Response response = client.newCall(request).execute();
+        String responseString = response.body().string();
+        return new ObjectMapper().readValue(responseString, ConvertedAmount.class).getTargetAmount();
+    }
+
+}