Define "waitForConfirmations" Hardhat task only once

[PaulRBerg]

In https://github.com/hifi-finance/hifi/commit/087d03b412ad3e1109d0d4f56dec631ffc15af93, we eliminated the tasks package, and moved the tasks in one of the smart contracts package (the one associated with each contract deployed).

One of the side-effects of that refactor was the massive duplication of the waitForConfirmations Hardhat task. It can be found in all smart contracts packages now.

We should find a way to avoid repeating ourselves and define this Hardhat task only once.