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`.