Migrate CARGO_REGISTRY_TOKEN to AztecBot

[johnathan79717]

Context

barretenberg-rs is now published on crates.io: https://crates.io/crates/barretenberg-rs

The CARGO_REGISTRY_TOKEN CI secret currently uses @johnathan79717's personal token. This should be migrated to AztecBot to avoid breakage if the personal token is revoked or the user leaves the org.

Steps

• Log into crates.io as AztecBot (via GitHub OAuth — requires access to the AztecBot GitHub account)
• Add AztecBot as a crate owner: cargo owner --add AztecBot barretenberg-rs
• Generate a crates.io API token from AztecBot's account (scope: publish-update, crate: barretenberg-rs)
• Update CARGO_REGISTRY_TOKEN in GitHub Actions master environment with AztecBot's token
• (Optional) Install crates.io GitHub App on AztecProtocol org and add github:AztecProtocol:crates-io-owners as a crate owner

Related

Follow-up from #1627