Add JSON Workbench to Online tools

[RashidHussain786]

Summary

Adds JSON Workbench to the Online tools section of awesome-json.

About JSON Workbench

JSON Workbench is a professional, browser-based web suite featuring:

• File & Data Comparer: Visual diffing and comparison between files.
• Base64 Tools: Fast Base64 encoding and decoding integrated with data processing.
• Formatter & Validator: Clean tree views, syntax highlighting, and instant validation.
• Privacy & Client-Side Processing: Processes data locally in the browser for privacy and speed.

Checklist

• Link follows format: * [JSON Workbench](https://josnworkbench.com/en) - Short description.
• Description does not contain the word "JSON" (per contribution guidelines).
• Description ends with a period.
• Checked for trailing whitespace.