Make ETH and STRK fee token addresses configurable

[kkovaacs]

There are custom Starknet chains where the fee token addresses diverge from the addresses used on the public Starknet integration/testnet/mainnet networks.

This issue leads to blockifier failing balance checks when executing transactions -- because the fee token address is not even deployed, we're basically reading a balance of zero for any contract address.

We should make the ETH and STRK fee token addresses configurable for at least the custom network use case.

[kkovaacs]

Starknet 0.13.4 has made token addresses available on the get_contract_addresses endpoint of the feeder gateway:

{
  "FriStatementContract": "0x55d049b4C82807808E76e61a08C6764bbf2ffB55",
  "GpsStatementVerifier": "0x2046B966994Adcb88D83f467a41b75d64C2a619F",
  "MemoryPageFactRegistry": "0x5628E75245Cc69eCA0994F0449F4dDA9FbB5Ec6a",
  "MerkleStatementContract": "0xd414f8f535D4a96cB00fFC8E85160b353cb7809c",
  "Starknet": "0x4737c0c1B4D5b1A687B42610DdabEE781152359c",
  "strk_l2_token_address": "0x4718f5a0fc34cc1af16a1cdee98ffb20c31f5cd61d6ab07201858f4287c938d",
  "eth_l2_token_address": "0x49d36570d4e46f48e99674bd3fcc84644ddd6b96f7c741b1562b82f9e004dc7"
}