Create entity integration mapping

curl --request POST \
  --url https://api.cloud.flexprice.io/v1/entity-integration-mappings \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "entity_id": "<string>",
  "entity_type": "customer",
  "provider_entity_id": "<string>",
  "provider_type": "<string>",
  "metadata": {}
}
'

{
  "created_at": "<string>",
  "created_by": "<string>",
  "entity_id": "<string>",
  "entity_type": "customer",
  "environment_id": "<string>",
  "id": "<string>",
  "provider_entity_id": "<string>",
  "provider_type": "<string>",
  "status": "published",
  "tenant_id": "<string>",
  "updated_at": "<string>",
  "updated_by": "<string>"
}