[FEATURE] Support for Dify Agents

[perzeuss]

Problem Statement

Currently, webhooks are limited to executing chatflows and workflows. I have received feedback from users who would like the ability to invoke agents via webhook. This is particularly important because agents currently lack support for blocking response mode (until #14784 is merged), making webhook integration even more valuable for seamless interactions.

Proposed Solution

Add new endpoint to invoke agents.

Impact

Users will be able to create webhooks for Dify agents and call agents with blocking mode.