This PR fixes issues on the L2 gaspricer pipeline:
If default price is not configured, oracle will automatically set default price to minimum base fee (10 gwei)
Likewise on X Layer gpcache initialization, if default price is not configured, cache will automatically set default price to DefaultXLayerPrice (1 gwei)
Better refactor lastPrice to defaultPrice on the oracle. lastPrice is never used in any pipeline now and we cannot assume that upstream will not change or use it. Since we want the dynamic GP checks on the dynamic price calculated to be checked against the default price, we should do this instead
Fix default gas price config to only be zkevm.default-gas-price
Summary
This PR fixes issues on the L2 gaspricer pipeline: