feat: add FeeToken interface

Author: johnletey

src/FeeToken.sol

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+pragma solidity >=0.8.13 <0.9.0;
+
+/// @title FeeToken
+/// @author NASD Inc.
+/// @notice An interface that must be implemented by any ERC20 that wants to be a supported fee token on Noble.
+interface FeeToken {
+    /// @notice Allows the system address to transfer tokens from one address to another.
+    function systemTransfer(address from, address to, uint256 amount) external returns (bool);
+}