Introduce logs for system contract updates

[greged93]

In order to easily monitor updates to the system contract, we should introduce logs on system contract updates. This is particularly interesting for the Rollup node in order to track authorized signer updates.

scroll-contracts/src/L1/system-contract/SystemConfig.sol

Lines 96 to 101 in 9e18444

	/// @notice Update the current signer.
	/// @param _newSigner The address of the new authorized signer.
	/// @dev Only the owner can call this function.
	function updateSigner(address _newSigner) external onlyOwner {
	currentSigner = _newSigner;
	}