Add a project variable

curl --request POST \
  --url {schemes}://api.upsun.com/projects/{projectId}/variables \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "<string>",
  "value": "<string>",
  "attributes": {},
  "is_json": true,
  "is_sensitive": true,
  "visible_build": true,
  "visible_runtime": true,
  "application_scope": [
    "<string>"
  ]
}
'

{
  "status": "<string>",
  "code": 123
}