Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/proxy/ERC1967/ERC1967Proxy.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.7.0) (proxy/ERC1967/ERC1967Proxy.sol)
+
+pragma solidity ^0.8.0;
+
+import "../Proxy.sol";
+import "./ERC1967Upgrade.sol";
+
+/**
+ * @dev This contract implements an upgradeable proxy. It is upgradeable because calls are delegated to an
+ * implementation address that can be changed. This address is stored in storage in the location specified by
+ * https://eips.ethereum.org/EIPS/eip-1967[EIP1967], so that it doesn't conflict with the storage layout of the
+ * implementation behind the proxy.
+ */
+contract ERC1967Proxy is Proxy, ERC1967Upgrade {
+    /**
+     * @dev Initializes the upgradeable proxy with an initial implementation specified by `_logic`.
+     *
+     * If `_data` is nonempty, it's used as data in a delegate call to `_logic`. This will typically be an encoded
+     * function call, and allows initializing the storage of the proxy like a Solidity constructor.
+     */
+    constructor(address _logic, bytes memory _data) payable {
+        _upgradeToAndCall(_logic, _data, false);
+    }
+
+    /**
+     * @dev Returns the current implementation address.
+     */
+    function _implementation() internal view virtual override returns (address impl) {
+        return ERC1967Upgrade._getImplementation();
+    }
+}