Learn guides: replace Truffle with Foundry #407
Description
Learn guides currently cover using Truffle or Hardhat.
Truffle is now sunset (https://consensys.io/blog/consensys-announces-the-sunset-of-truffle-and-ganache-and-new-hardhat) and Foundry usage is at 32% (https://soliditylang.org/blog/2024/04/03/solidity-developer-survey-2023-results/)
Learn guides should be updated to replace Truffle with Foundry.
### Tasks
- [ ] https://github.com/OpenZeppelin/docs.openzeppelin.com/pull/418
- [ ] Add Foundry to Learn guides