* contracts-bedrock: add forge contract verification support

Add etherscan contract verification for the hh/foundry
compiler toolchain. This will eventually be upstreamed,
but is implemented here to ensure that it works thoroughly
first.

To run the task:

```
export ETHERSCAN_API_KEY=$(cat api-key.txt)
$ npx hardhat forge-verify --network goerli
```

In the future, other contract verification backends
will be added to forge and this task will be updated
to support them.

Example contract that was verified: https://goerli.etherscan.io/address/0x1234662682c85fa6fb375416d14db965eba222ba#code

An individual contract can be targeted instead of all of them
with the `--contract` flag. If hardhat deploy has configured
external deployments, forge will not be able to verify them.
It may be possible to implement that in the future.

* contracts-bedrock: modularize tasks