fix: Bump L2 gas limit for L1 -> L2 zkSync messages (#334)

Testing on the era testnet shows that typical messaging consumes up
around 1M gas on L2.

Author: pxrl

contracts/chain-adapters/ZkSync_Adapter.sol

@@ -129,7 +129,7 @@ contract ZkSync_Adapter is AdapterInterface {
     // goes live. For now, we'll hardcode these and use aggressive values to ensure inclusion.
 
     // Limit on L2 gas to spend.
-    uint256 public constant L2_GAS_LIMIT = 300_000;
+    uint256 public constant L2_GAS_LIMIT = 2_000_000;
 
     // How much gas is required to publish a byte of data from L1 to L2. 800 is the required value
     // as set here https://github.com/matter-labs/era-contracts/blob/6391c0d7bf6184d7f6718060e3991ba6f0efe4a7/ethereum/contracts/zksync/facets/Mailbox.sol#L226