Improve how we detect that we are using the native ERC20 feature in zksync-cli

[juanbono]

🌟 Feature Request

📝 Description

In #21 we are using environment variables (set according to the contents of the etc/tokens/native_erc20.json file.
We should use a more robust approach, we could use the zk_getBaseTokenAddress for this.

🤔 Rationale

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🖼️ Mockups/Examples

If applicable, provide mockups or examples of how the feature would work.

📋 Additional Context

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