Use 'rustup' brew dependency for Octez brew formula.

What

'rustup-init.sh' script doesn't work correctly when trying to build Octez formula for x86_64 on aarch64 using Rosetta and install aarch64 version of the compiler despite the fact that build is x86_64.

Unlike 'rustup install' which detects the architecture correctly.

Why

Currently, it's impossible to build a formula targeting x86_64 on an aarch64 machine.

How

Use rustup instead of rustup-init.sh

Manually testing the MR

arch -x86_64 /usr/local/bin/brew install --formula ./octez.rb

Make sure that you installed brew under Rosetta as well.

arch -x86_64 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR