feat: Allow to specify registry & factory to avoid re-deploying.

[Mc01]

Upstreaming changes present in deployment of OpSuccinct to Celo networks: celo-org#11

Introduced:

• .env.example as template for .env
• optional creation of registry, factory & superchain config
• extracted fetching of config into separate recipe in justfile
• introduced deploying of contracts with custom config without fetching in justfile