indexer: support public alpha testnet

[tuxcanfly]

Description

This PR adds support for the public alpha testnet on Goerli.

Tests

Only updates the contract addresses and chain id.

Additional context

Need help from @optimisticben to deploy an instance.

[changeset-bot]

⚠️ No Changeset found

Latest commit: af92ef4

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[mergify]

This PR changes implementation code, but doesn't include a changeset. Did you forget to add one?