You can use JSON.stringify to look for equality in the addons object and then merge your objects. Like this:

const array = [
  {
    "metric1": 4.1,
    "addons": {
      "call_uuid_1": "13d1e097-0363-4a81-b9e4-85c6a770cdb2",
      "ThisDN_1": "50002",
      "call_uuid": "13d1e097-0363-4a81-b9e4-85c6a770cdb4",
      "ThisDN": "50004"
    }
  },
  {
    "metric2": -12345.123412341234,
    "addons": {
      "call_uuid_2": "13d1e097-0363-4a81-b9e4-85c6a770cdb3",
      "ThisDN_2": "50003",
      "call_uuid": "13d1e097-0363-4a81-b9e4-85c6a770cdb4",
      "ThisDN": "50004"
    }
  },
  {
    "metric3": -2345.123412341234,
    "addons": {
      "call_uuid_1": "13d1e097-0363-4a81-b9e4-85c6a770cdb2",
      "ThisDN_1": "50002",
      "call_uuid": "13d1e097-0363-4a81-b9e4-85c6a770cdb4",
      "ThisDN": "50004"
    }
  },
  {
    "metric4": -345.12341234123414,
    "addons": {
      "call_uuid_2": "13d1e097-0363-4a81-b9e4-85c6a770cdb3",
      "ThisDN_2": "50003",
      "call_uuid": "13d1e097-0363-4a81-b9e4-85c6a770cdb4",
      "ThisDN": "50004"
    }
  }
];

const mergedArray = [];
const addonsToIndexMap = {};

array.forEach(item => {
 const stringifyAddon = JSON.stringify(item.addons);    
 let indexInTheMap = addonsToIndexMap[stringifyAddon];
 if(indexInTheMap !== undefined) {
   mergedArray[indexInTheMap] = {...mergedArray[indexInTheMap], ...item};
 } else {
   mergedArray.push(item);
   addonsToIndexMap[stringifyAddon] = mergedArray.length - 1;
 }
});
console.log(mergedArray);

The use of addonsToIndexMap is just for optimization purposes. Note: This method only works if the order of keys within the addon objects is the same. Also, I rectified the input in my program to update the key call_uuid_l with call_uuid_1 to get the expected output, as mentioned in the comments. Please modify it accordingly.

If the array has more than one element with the same addons object, you can delete the first one's addons object and then merge it with the others.

for (let i = 0; i < arr.length; i++) {
  for (let j = i + 1; j < arr.length; j++) {
    if (JSON.stringify(arr[i]["addons"]) === JSON.stringify(arr[j]["addons"])) {
      delete arr[i]["addons"];
      Object.assign(arr[i], arr[j]);
      arr.splice(j, 1);
      j -= 1;
    }
  }
}

Output:

[
  {
    metric1: 4.1,
    metric3: -2345.123412341234,
    addons: {
      call_uuid_1: '13d1e097-0363-4a81-b9e4-85c6a770cdb2',
      ThisDN_1: '50002',
      call_uuid: '13d1e097-0363-4a81-b9e4-85c6a770cdb4',
      ThisDN: '50004'
    }
  },
  {
    metric2: -12345.123412341234,
    metric4: -345.12341234123414,
    addons: {
      call_uuid_2: '13d1e097-0363-4a81-b9e4-85c6a770cdb3',
      ThisDN_2: '50003',
      call_uuid: '13d1e097-0363-4a81-b9e4-85c6a770cdb4',
      ThisDN: '50004'
    }
  }
]