Support ${VAR} env var resolution in RPC URLs

[ejacquier]

Summary

• Allow ${VAR_NAME} syntax in RPC URLs in project.yaml that resolves from environment variables (loaded from .env or shell), keeping
  secrets out of version control
• Resolve env vars in all RPC URL paths: loadWorkflowSettings, GetRpcUrlSettings, and GetExperimentalChains
• Add redacted RPC URL logging in verbose mode for debugging (https://rpc.example.com/***)

Usage

  # project.yaml (committed)
  staging-settings:
    rpcs:
      - chain-name: ethereum-testnet-sepolia
        url: https://rpc.example.com/${CRE_SECRET_RPC_SEPOLIA}

# .env (gitignored)
 CRE_SECRET_RPC_SEPOLIA=my-secret-api-key

[github-actions]

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