Upsert customer

curl --request PUT \
  --url https://api.openint.dev/v0/core/customer/{id} \
  --header 'Content-Type: application/json' \
  --header 'x-apikey: <api-key>' \
  --header 'x-connection-id: <api-key>' \
  --data '{
  "metadata": "<any>"
}'

{
  "id": "<string>",
  "orgId": "<string>",
  "metadata": "<any>"
}