fix: add base token address to hyperchain config

[sanekmelnikov]

What ❔

Adding missing baseTokenAddress to the hyperchain configuration. Adding a fallback to use the default L2 base token address if it's not specified in the config.

Why ❔

When configuring the block explorer using npm run hyperchain:configure, the resulting configuration was missing the baseTokenAddress value. This absence was causing an error here. As a result of this error, the system was defaulting to Sepolia (which I assume is not the intended behavior for your hyperchain setup).

Checklist

• [x] PR title corresponds to the body of PR (we generate changelog entries from PRs).
• [x] Tests for the changes have been added / updated.
• [x] Documentation comments have been added / updated.

[vasyl-ivanchuk]

These changes are merged in this PR.