feat: Add initial contract to validate operations

contracts/interfaces/IOperationalValidator.sol

@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: agpl-3.0
+pragma solidity 0.8.7;
+
+interface IOperationalValidator {
+  function isBorrowAllowed() external returns (bool);
+
+  function isLiquidationAllowed() external returns (bool);
+}

contracts/protocol/configuration/OperationalValidator.sol

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: agpl-3.0
+pragma solidity 0.8.7;
+
+import {IPoolAddressesProvider} from '../../interfaces/IPoolAddressesProvider.sol';
+import {IOperationalValidator} from '../../interfaces/IOperationalValidator.sol';
+
+/**
+ * @title OperationalValidator
+ * @author Aave
+ * @notice
+ */
+contract OperationalValidator is IOperationalValidator {
+  IPoolAddressesProvider public _addressesProvider;
+  uint256 public _gracePeriod;
+
+  /**
+   * @notice Constructor
+   * @dev
+   * @param provider The address of the PoolAddressesProvider
+   */
+  constructor(IPoolAddressesProvider provider, uint256 gracePeriod) {
+    _addressesProvider = provider;
+    _gracePeriod = gracePeriod;
+  }
+
+  /// @inheritdoc IOperationalValidator
+  function isBorrowAllowed() public override returns (bool) {
+    // If the sequencer goes down, borrowing is not allowed
+  }
+
+  /// @inheritdoc IOperationalValidator
+  function isLiquidationAllowed() public override returns (bool) {
+    // If the sequencer goes down AND HF > 0.9, liquidation is not allowed
+    // If timestampSequencerGotUp - block.timestamp > gracePeriod, liquidation allowed
+  }
+}