docs: dify docs (#2254)

A new PR for dify docs based on the:
#2037 with new screenshots and
fixes from the PR comments.
We can close the old PR and keep this one. 

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Documentation-only change adding a new integration guide; primary risk
is broken links or outdated UI screenshots.
> 
> **Overview**
> Adds new docs page `integrations/dify` describing how to connect Apify
with Dify via the `apify-integration` plugin.
> 
> Covers authentication (API token/OAuth), using Apify as workflow
actions (run Actor/task, scrape URL, fetch dataset/KV store), and
setting up webhook triggers from Apify to Dify, including guidance on
Dify’s flattened variable naming for nested webhook payload fields
(e.g., `resource__defaultDatasetId`).
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
aba66ef. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: jakcinmarina