Add Governor contracts (#2672)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/governance/extensions/IGovernorTimelock.sol

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../IGovernor.sol";
+
+/**
+ * @dev Extension of the {IGovernor} for timelock supporting modules.
+ *
+ * _Available since v4.3._
+ */
+interface IGovernorTimelock is IGovernor {
+    event ProposalQueued(uint256 proposalId, uint256 eta);
+
+    function timelock() external view returns (address);
+
+    function proposalEta(uint256 proposalId) external view returns (uint256);
+
+    function queue(
+        address[] calldata targets,
+        uint256[] calldata values,
+        bytes[] calldata calldatas,
+        bytes32 descriptionHash
+    ) external returns (uint256 proposalId);
+}