l2geth: allow 0 gasprice txs for `OVM_GasPriceOracle.owner`

This PR allows the owner of the `OVM_GasPriceOracle` to send
transactions with 0 gas price when the enforce fees config option
is turned on.

The L2 gas price is currently updated by sending transactions to the
chain to a special contract. In the future it should be updated as a
side effect of transaction execution. Having the gas price on chain is
important so that it can be replicated accross the network to ensure
that users can send transactions with a high enough fee.

Having the `OVM_GasPriceOracle.owner` key not need to maintain
ETH on L2 is an operational simplification as well prevents a
terrible scenario where a bug causes the L2 gas price to go so high
that it is impossible for the owner to update it.

l2geth: sequencer fee buffer

The fees are currently calculated as a sum of the L1 fee and the L2 fee
where the L1 fee is the approximate cost of the batch submission of the
transaction (L1 gas price * L1 gas used) and the L2 fee is the
approximate cost of the execution on L2 taking into account congestion
(L2 gas price * L2 gas limit).

When either the L1 or L2 gas price is volatile, it can result in the
quote that the user receives from `eth_estimateGas` to be rejected
as the fee that the Sequencer is expecting has gone up.

This PR adds logic to set a buffer in either direction of the current
price that will allow the sequencer to still accept transactions within.

Two new config options are added:

- `--rollup.feethresholddown` or `ROLLUP_FEE_THRESHOLD_DOWN`
- `--rollup.feethresholdup` or `ROLLUP_FEE_THRESHOLD_UP`

Note that these config options are only useful for when running
in Sequencer mode, they are not useful for replicas/verifiers.
This is because the Sequencer is the only write node in the network.

These config options are interpreted as floating point numbers and are
multiplied against the current fee that the sequencer is expecting.
To allow for a downward buffer of 10% and an upward buffer of 100%,
use the options:

- `ROLLUP_FEE_THRESHOLD_DOWN=0.9`
- `ROLLUP_FEE_THRESHOLD_UP=2`

This will allow for slight fee volatility downwards and prevent users
from excessively overpaying on fees accidentally.

This is a UX and profit tradeoff for the sequencer and can be exploited
by bots. If bots are consistently taking advantage of this, the max
threshold down will have to be calibrated to what the normal fee is
today.

Both config options are sanity checked in the `SyncService` constructor
and will result in errors if they are bad. The threshold down must
be less than 1 and the threshold up must be greater than 1.

Version Packages

feat[integration-tests]: add basic stress tests

ci: release latest image tags on release

Develop To Master PR

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