Add object deep merge utility function

src/util.js

@@ -196,6 +196,27 @@ async function readAllChunks(readableStream) {
     });
 }
 
+function isObject(item) {
+    return (item && typeof item === 'object' && !Array.isArray(item));
+}
+
+function deepMerge(target, source) {
+    let output = Object.assign({}, target);
+    if (isObject(target) && isObject(source)) {
+        Object.keys(source).forEach(key => {
+            if (isObject(source[key])) {
+                if (!(key in target))
+                    Object.assign(output, { [key]: source[key] });
+                else
+                    output[key] = deepMerge(target[key], source[key]);
+            } else {
+                Object.assign(output, { [key]: source[key] });
+            }
+        });
+    }
+    return output;
+}
+
 module.exports = {
     getConfig,
     getConfigValue,
@@ -205,4 +226,5 @@ module.exports = {
     getImageBuffers,
     readAllChunks,
     delay,
+    deepMerge,
 };