feat(validator): L2 gas validation

[t00ts]

Apollo is scraping L1 gas prices from Ethereum and L2 gas prices are determined based on that as far as I understand. We should find out the algorithm (average of the latest N L1 blocks?) and implement a scraper ourselves so that we can validate the gas prices.

(https://github.com/starkware-libs/sequencer/tree/main/crates/apollo_l1_gas_price)

Originally posted by @kkovaacs in #3159 (comment)