fix: lint deploy-l2 folder in contracts

dtl: configurable gas price backend

Adds a new config option `--l1-gas-price-backend` or
`DATA_TRANSPORT_LAYER_L1_GAS_PRICE_BACKEND` that can be set to `l1` or
`l2`. This impacts the behavior of the HTTP endpoint `GET /eth/gasprice`
by changing what is queried to return the L1 gas price. The L1 gas price
is required to compute the L2 fee since the L2 fee consists of
`L1 gas price * L1 gas used + L1 gas price * L2 gas limit`. If the L1
gas price differs too much between different L2 providers, then users
using `eth_estimateGas` may submit transactions with too low of a fee
and be unable to submit transactions to the sequencer.

By configuring the DTL to use L2 as the L1 gas price backend, it will
call the Sequencer's RPC endpoint `rollup_gasPrices` which returns the
L1 and L2 gas prices from the point of view of the sequencer. The L2 gas
price exists in the state, so that will always be the same between the
sequencer and any replicas. The L1 gas price does not live on chain, so
querying for it from the sequencer directly will ensure that users send
transactions with a fee that is large enough.

Also adds eth/gasprice info to README.

Merge pull request #1033 from ethereum-optimism/elena/op-790-add-linting-andor-formatting-to-solidity

Add contracts linting

which changes the way it parses errors from returndata
Fix provided by @smartcontracts

https://github.com/ethereum-optimism/optimism/pull/1033#issuecomment-866146467

Removed unused functions from core utils

docker: pin to alpine 3.13 for l2geth

fix: update statement for skipping codechecks

A bug has appeared when older versions of Docker are used to build
alpine based images in alpine version 3.14. To prevent this problem
from happening to the users, this PR pins the version to 3.13.

The observed problem is that `make` cannot run any command and
the error message states `Operation not permitted.` Removing
`make` was one way to solve the problem but that would increase
the diff from upstream geth.

See these links for details:
https://github.com/alpinelinux/docker-alpine/issues/182
https://wiki.alpinelinux.org/wiki/Release_Notes_for_Alpine_3.14.0

github actions: bump geth CI golang version

fix: skip codechecks for PRs from external repos

and fix a solidity linting error

compliant with the standard bridge