feat: adds config-out cli option

[dutterbutter]

What 💻

• Added a new CLI option --config-out to specify an output file for JSON configuration.
• Introduced a config_out field in the TestNodeConfig struct to handle output file specification.
• Updated configuration handling with new methods: as_json for JSON conversion and set_config_out for setting the output file.
• Updated the print method in TestNodeConfig to write configuration to the specified JSON file if config_out is set.

Why ✋

• Aligns with Anvil CLI options
• To provide users with the ability to export configuration settings as a JSON file for easier debugging and external processing.

Evidence 📷

Usage examples:

1. Exporting configuration during a fork command:

   ./target/release/era_test_node --config-out text.json fork --network mainnet

2. Exporting configuration during a run command:

   ./target/release/era_test_node --config-out text.json run

Output:

• A JSON file (text.json) is created with the current configuration details after execution.