Is your feature request related to a problem? Please describe.
L2Geth needs access to the current congestion price. This value is stored in the state of L2 & must be retrieved to calculate the fee as defined in #823

Describe the solution you'd like
Update the L2FeeOracle in L2Geth to query the congestion price oracle contract that was created in #908. If desired, this can be done periodically & cached in the RPC to provide efficient fee calculations.

Blocked by
#908