Add new validator registration workflow with script and dapp

[pepae]

This PR introduces a streamlined validator registration workflow with the following features:

• A Dockerized script to generate validator keys, registration signatures, and configuration files.
• A React-based DApp for submitting registration signatures to the Gnosis Chain smart contract.
• Preconfigured .env.example files for both the script and the DApp to simplify setup.
• Optional instructions for uploading registration files when the DApp and script run on separate machines.