add Available since 4.1 comments

(cherry picked from commit 9a698e6b7b)

contracts/proxy/ERC1967/ERC1967Storage.sol

@@ -9,6 +9,8 @@ import "../../utils/StorageSlot.sol";
 /**
  * @dev This abstract contract provides setters and getters for the different
  * https://eips.ethereum.org/EIPS/eip-1967[EIP1967] storage slots.
+ *
+ * _Available since v4.1._
  */
 abstract contract ERC1967Storage {
     /**

contracts/proxy/ERC1967/ERC1967Upgrade.sol

@@ -8,6 +8,8 @@ import "./ERC1967Storage.sol";
  * @dev This abstract contract provides event emitting update functions for
  * https://eips.ethereum.org/EIPS/eip-1967[EIP1967] slots.
  *
+ * _Available since v4.1._
+ *
  * @custom:oz-upgrades-unsafe-allow delegatecall
  */
 abstract contract ERC1967Upgrade is ERC1967Storage {

contracts/proxy/utils/UUPSUpgradeable.sol

@@ -10,6 +10,8 @@ import "../ERC1967/ERC1967Upgrade.sol";
  * continuation of the upgradability.
  *
  * The {_authorizeUpgrade} function MUST be overridden to include access restriction to the upgrade mechanism.
+ *
+ * _Available since v4.1._
  */
 abstract contract UUPSUpgradeable is ERC1967Upgrade {
     function upgradeTo(address newImplementation) external virtual {