Bulk update contacts

We now allow users to pass a set of contacts with their updated fields in one single API call via a JSON payload.
Each contact can have different fields overwriten/updated through this call.
In a single call each contact can be identified with a mix of id or email or sms

Example

curl --request POST \
     --url https://api.sendinblue.com/v3/contacts/batch \
     --header 'Accept: application/json' \
     --header 'Content-Type: application/json' \
     --data '
{
     "contacts": [
          {
               "attributes": {
                    "flagged": "true"
               },
               "listIds": [
                    12
               ],
               "email": "[email protected]",
               "emailBlacklisted": false
          },
          {
               "attributes": {
                    "flagged": "false",
                    "FNAME": "John"
               },
               "id": 543
          }
     ]
}
'