Create an account relationship

curl --request POST \
  --url https://platform.thena.ai/v1/accounts/relationships \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '{
  "accountId": "A123",
  "relatedAccountId": "A124",
  "relationshipType": "RELATIONSHIP_TYPE_PARENT",
  "metadata": {}
}'

{
  "id": "AR123",
  "accountId": "<string>",
  "account": "<string>",
  "relatedAccountId": "<string>",
  "relatedAccount": "<string>",
  "relationshipType": {
    "id": "ART123",
    "name": "Parent",
    "inverseRelationshipId": "ART124",
    "inverseRelationship": "Subsidiary",
    "createdAt": "<string>",
    "updatedAt": "<string>",
    "metadata": {}
  },
  "createdAt": "<string>",
  "updatedAt": "<string>",
  "metadata": {}
}