List customers

curl --request GET \
  --url https://api.useaira.com/v1/customers/ \
  --header 'X-API-KEY: <api-key>'

{
  "items": [
    {
      "id": "<string>",
      "externalId": "705faf65-9c8b-4053-8c0b-2021281ce83f",
      "name": "Acme Inc.",
      "customFields": {
        "customField1": "value1",
        "customField2": [
          "value2",
          "value3"
        ]
      }
    }
  ],
  "hasMore": true
}