Prevent creating duplicate contacts in the contacts/batch/new

[alanhartless]

Q	A
Bug fix?	y
New feature?
Automated tests included?
Related user documentation PR URL
Related developer documentation PR URL
Issues addressed (#s or URLs)
BC breaks?
Deprecations?

Description:

The api/contact/new endpoint will update a contact if a unique identifier field matched instead of creating a new. But the batch endpoint created all new contacts regardless. This PR makes the batch endpoint act the same as the single contact endpoint.

Steps to reproduce the bug:

1. Post the following payload to api/contacts/batch/new

[
  {
    "email": "email1@email.com",
    "firstname": "BatchUpdate"
  },
  {
    "email": "email2@email.com",
    "firstname": "BatchUpdate2"
  },
  {
    "email": "email3@email.com",
    "firstname": "BatchUpdate3"
  }
]

2. Post it again and notice that the three contacts will be created again.

Steps to test this PR:

1. Delete the contacts then repeat. This time the second post will update the contacts instead of creating new.

[javjim]

Tested and workin properly, was able to reproduce bug, and verify fix

[escopecz]

Works as described 👍