Convention creation

curl --request POST \
  --url https://api.opx.co/partners/v1/conventions \
  --header 'Content-Type: application/json' \
  --data '{
  "contract_template_id": 123,
  "installer_siret": "<string>",
  "installer_contact_email": "jsmith@example.com"
}'

{
  "data": {
    "id": 123,
    "contract_template_id": 123,
    "reference": "<string>",
    "rai_name": "<string>",
    "status": "<string>",
    "installer_name": "<string>",
    "signed_date": "<string>",
    "start_date": "<string>",
    "end_date": "<string>",
    "incentive_type": "<string>",
    "classic_volume": "<string>",
    "precarity_volume": "<string>"
  }
}