Update an end user (auto-merges on org_external_end_user_id conflict)

curl --request PUT \
  --url https://api-sandbox.featherhq.com/v1/identity/end-users/{end_user_id} \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "display_name": "<string>",
  "primary_email": "<string>",
  "primary_phone": "<string>",
  "metadata": {},
  "org_external_end_user_id": "<string>"
}
'

{
  "uid": "<string>",
  "org_id": "<string>",
  "status": "<string>",
  "display_name": "<string>",
  "primary_email": "<string>",
  "primary_phone": "<string>",
  "metadata": {},
  "org_external_end_user_id": "<string>",
  "merged_into": "<string>"
}