Add new end entity, if it does not exist

Example request

{
  "username": "JohnDoe",
  "password": "foo123",
  "subject_dn": "CN=John Doe,SURNAME=Doe,GIVENNAME=John,C=SE",
  "subject_alt_name": "rfc822Name=john.doe@example.com",
  "email": "john.doe@example.com",
  "extension_data": [
    {
      "name": "1.3.6.1.5.5.7.1.24/customdata_STARTTIME",
      "value": "3003020105/2022-12-13 00:00:00"
    }
  ],
  "custom_data": [
    {
      "name": "1.3.6.1.5.5.7.1.24/customdata_STARTTIME",
      "value": "3003020105/2022-12-13 00:00:00"
    }
  ],
  "ca_name": "ExampleCA",
  "certificate_profile_name": "ENDUSER",
  "end_entity_profile_name": "ExampleEEP",
  "token": "P12",
  "account_binding_id": "1234567890",
  "status": "NEW",
  "start_time": "ISO 8601 Date string, eg. '2023-06-15 14:07:09'",
  "end_time": "ISO 8601 Date string, eg. '2023-06-15 14:07:09'",
  "certificate_serial_number": 1234567890,
  "card_number": "1234567890"
}