[Chronik] Check rustup-init.sh hash before executing

Summary: Currently we just download a shell script from the interwebs and execute it, which is not good

Test Plan: ./install-dependencies-bullseye.sh in the ABC docker container

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15551