I tried using dialogflow-fulfillment library but I guess it is for Dialogflow ES so now I am using @google-cloud/dialogflow-cx library but I don't know how to use this library for webhook connection to reply to users using fulfilments, there is very little material available for Dialogflow CX.
// use credentials or keyFilename i'm using keyFile
    credentials: {
        private_key: "-----BEGIN PRIVATE KEY-----==\n-----END PRIVATE KEY-----\n",
 
        client_email:"pro1a3711.iam.gserviceaccount.com",
    },                                                                                                                                                                                                                                                                                                                                                                              
        keyFilename: './pr.json'
}
const {SessionsClient} = require('@google-cloud/dialogflow-cx');
const projectId = 'pro1-293711';
const location = 'global';
const agentId = 'da2271f5-0221-4dce-98d3-efa----9dd';
const languageCode = 'en';
 const query = ['hello'];
// Imports the Google Cloud Some API library
//console.log(WebhooksClient)
const client = new SessionsClient(config);
   //console.log("client",client)
     async function detectIntentText() {
        const sessionId = Math.random().toString(36).substring(7);
    const sessionPath = client.projectLocationAgentSessionPath(
      projectId,
      location,
      agentId,
      sessionId
    );
    console.info(sessionPath);
    const request = {
        session: sessionPath,
        queryInput: {
          text: {
            text: query,
          },
          languageCode,
        },
      };
      const [response] = await client.detectIntent(request);
      console.log(`User Query: ${query}`);
      for (const message of response.queryResult.responseMessages) {
        if (message.text) {
          console.log(`Agent Response: ${message.text.text}`);
        }
      }
      if (response.queryResult.match.intent) {
        console.log(
          `Matched Intent: ${response.queryResult.match.intent.displayName}`
        );
      }
      console.log(
        `Current Page: ${response.queryResult.currentPage.displayName}`
      );
    }
 detectIntentText()```