Add EnvConfig parser

[lemunozm]

Product requirements

• Add EnvConfig parser as a source of truth for validating env/*.json files.
• Benefits:
  • Allows to always parse the env files with same expectations and do proper checks.
  • Allows to check that all env files are consitent with our requirements (see EnvFiles.t.sol).
  • Allows a much easier integration of env files with our codebase.
    • Right now integrated to ValidateContractsFromFactories.s.sol script but the long term of this is to integrate also in LaunchDeployer, OnlyAdapters, spells, validators, and fork tests (follow up PRs)