fix: Add contract to handle IOU

contracts/src/v0.8/ccip/pools/GhoIOU.sol

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: BUSL-1.1
+pragma solidity ^0.8.0;
+
+import {ITypeAndVersion} from "../../shared/interfaces/ITypeAndVersion.sol";
+import {ILiquidityContainer} from "../../rebalancer/interfaces/ILiquidityContainer.sol";
+
+import {TokenPool} from "./TokenPool.sol";
+import {RateLimiter} from "../libraries/RateLimiter.sol";
+
+import {IERC20} from "../../vendor/openzeppelin-solidity/v4.8.3/contracts/token/ERC20/IERC20.sol";
+import {SafeERC20} from "../../vendor/openzeppelin-solidity/v4.8.3/contracts/token/ERC20/utils/SafeERC20.sol";
+
+import {console2} from "forge-std/console2.sol";
+
+contract GhoIOU { // TODO: Upgradeable
+  mapping(address => uint256) pendingBalance;
+
+  function setPendingBalance(address user, uint256 amount) public {
+    // TODO: onlyOwner
+    pendingBalance[user] = amount;
+
+    // TODO: event
+  }
+
+  function getPendingBalance(address user) public view returns (uint256) {
+    return pendingBalance[user];
+  }
+
+  function sendIOU() public {
+    // TODO: Send arbitrary message to destination TokenPool
+    // This must pay with feeToken (native or LINK for now)
+    // TODO: check supported network
+  }
+}