feat(specs,fixtures,tests): New Spec/Fixture type: ConfigSpec

[marioevz]

🗒️ Description

Draft that contains the configuration fixture type to be consumed by clients to verify their network configuration.

I think everything needs to be moved to ethereum_test_forks.

We can have a BaseFork.network_config method to retrieve the cumulative configuration fields that should go into each network configuration.

🔗 Related Issues

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• Tests: All converted JSON/YML tests from ethereum/tests have been added to converted-ethereum-tests.txt.
• Tests: A PR with removal of converted JSON/YML tests from ethereum/tests have been opened.
• Tests: Included the type and version of evm t8n tool used to locally execute test cases: e.g., ref with commit hash or geth 1.13.1-stable-3f40e65.
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.