curl --request POST \
  --url https://eu-gcp-api.vg-stuff.com/v3/agents/{agentId}/variables \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "variable": {
    "in": "<string>",
    "type": "string",
    "value": "<any>",
    "defaultValue": "<any>",
    "key": "<string>",
    "description": "<string>",
    "required": true,
    "reusable": true,
    "isEnv": true,
    "isSystem": true,
    "isGlobal": true
  }
}'

{
  "success": true,
  "message": "<string>",
  "data": {
    "id": "<string>",
    "in": "<string>",
    "type": "string",
    "value": "<any>",
    "defaultValue": "<any>",
    "key": "<string>",
    "description": "<string>",
    "required": true,
    "reusable": true,
    "isEnv": true,
    "isSystem": true,
    "isGlobal": true,
    "agentId": "<string>",
    "userId": "<string>"
  }
}