- Adopts Go workspaces for future compatibility with the Bedrock move into the monorepo
- Moves Go packages to the root of the repo in order to fix import paths
- Rewrites existing Go import paths
- Removes Stackman, since it's not needed anymore
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Compute the gas used in an epoch based on the
actual amount of gas used instead of assuming
that the full block's worth of gas was used in
each block.

The `gas-price` metric was renamed to `gas_price`
as using a `-` is invalid syntax in a prometheus metric.

Fixes https://github.com/ethereum-optimism/optimism/issues/1819

The `gas-oracle` will now periodically ping L1 asking
for the latest header and will update the `l1BaseFee`
value in the `OVM_GasPriceOracle` oracle predeploy when
the base fee changes more than a configurable amount.

This is very similar to the way that the `gas-oracle` sets
the L2 gas price based on the amount of gas that has
been used in an amount of time.

Note that this is a breaking change when it comes to config.
Some config options are renamed and some config options are added.

`--ethereum-http-url` now corresponds to the L1 URL and
`--layer-two-http-url` corresponds to the L2 URL. Previously,
only an L2 URL was provided and it was called `--ethereum-http-url`.

Now there are flags for `--l1-chain-id` and `--l2-chain-id` when
previously `--chain-id` corresponded to the L2 chain id.

There are also now flags for turning on and off functionality.
`--enable-l1-base-fee` and `--enable-l2-gas-price` are used
to turn on updating of the corresponding values. They are on by
default.

The `--l1-base-fee-significant-factor` is expected to be a decimal
and determines how much the base fee on L1 must change before the
`gas-oracle` will consider updating the base fee by sending
a transaction to the `OVM_GasPriceOracle`.

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.