Add Robot Framework Solidity Testing Toolkit

[jg8481]

This will add the following Robot Framework toolkit that combines Truffle and Hardhat with RPA.

https://github.com/jg8481/Robot-Framework-Solidity-Testing-Toolkit

Checklist

• The URL is not already present in the list (check with CTRL/CMD+F in the raw markdown file).
• Each description starts with an uppercase character and ends with a period.
  Example: solc-js - JavaScript bindings for the compiler.
• Drop all A / An prefixes at the start of the description.
• Avoid using the word Solidity in the description.