Automate Hardhat 2 release and harden the process against NPM attacks

[michalbrabec]

The release of Hardhat 2 is still done from a local workstation instead of an automated pipeline or action. We must automate the process and migrate it to CI to minimise the effort needed to release new versions and reduce the risk of a compromised workstation compromising the release. Proof of presence or multi-sign might be needed to prevent NPM attacks.