Use merge instead of replace

[cakeinpanic]

Hi, great action!
I'm trying to use it in my project to add dependencies to my package.json, but now they are getting fully replaced

Would be cool to have an input to optionally merge objects
Current behaviour:

 "devDependencies": {
-   "globby": "^13.1.4",
+  "husky": "7.0.4"
 },

desired behaviour:

"devDependencies": {
     "globby": "^13.1.4",
+    "husky": "7.0.4"
  },

when input file is

{
 "devDependencies": {
    "husky": "7.0.4"
  }
}

[fiddlermikey]

Thanks for the input. I can see where this would be useful. I also plan to add the ability to delete an object from the json file. It really should be fully CRUD capable. Feel free to contribute code