feat[integration-tests]: add basic stress tests

ci: release latest image tags on release

feat[geth]: add gas pricer for congestion fees

contracts: add set-l2-gasprice task

Adds a dockerfile for the `gas-oracle` as well as adding it as
a service in the `docker-compose.yaml`. It is not enabled by
default due to memory issues in CI already happening occasionally
where the integration tests are oom killed.

The `gas-oracle` is configured with a key that owns the
`OVM_GasPriceOracle`.

This PR adds the `gas-oracle` to the Github Actions
workflow that is responsible for publishing the docker images.

This commit adds the `gas-oracle` which is an offchain entity
that sends transactions to L2 to update the gas price. It must
be configured with a private key as the `OVM_GasPriceOracle`
is owned.

The `gas-oracle` is added to the changesets setup.

Tests are included as well as CI. Dockerizing will happen
in a follow up PR.

The `gasprices` package implements the logic that updates
L2 gasprices on the Optimistic Ethereum Network.
Co-authored-by: Karl Floersch <karl@karlfloersch.com>

feat: add workflow for running SNX test suite

chore(ci): Skip check files job on push events

Version Packages

Merge develop to master

ci(contracts): only run codecov if contracts package is modified

In order to skip running the CodeCov job when it isn't relevant, a new job was added to the ts-packges workflow. For a PR, this job identifies all the files modified between the base branch and the tip of the PR branch, and writes to a variable which can be used to decide if subsequent jobs should run.

Github Actions provides an easy method for achieving this at the level of a workflow, but not for specific jobs within a workflow.

Add op_exporter for sequencer metrics and health endpoint

l2geth: use `hexutil.Big` to prevent overflows

The `RollupClient` decodes the JSON from the DTL as a uint64,
this updates it to be a `big.Int`

Includes a test for the value field that ensures it does not overflow

Increase client_body_buffer_size for rpc-proxy

Added client_max_body_size to rpc-proxy config

feat[integration-tests]: make integration tests work against production networks

Version Packages

feat: update README to include info about rebasing

Added metric for sequencer health
Added Dockerfile for op_exporter;
Fixed Dockerfile path

fix: update CI to avoid running out of memory

Merge develop into master

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