Add hardhat-verify dependency to verify TokenStaking

Deployment and verification steps:

> npx hardhat deploy --tags TokenStaking --network mainnet
> npx hardhat verify --network mainnet <IMPLEMENTATION_ADDRESS> "0xcdf7028ceab81fa0c6971208e83fa7872994bee5"

Author: cygnusv

hardhat.config.ts

@@ -102,6 +102,11 @@ const config: HardhatUserConfig = {
     pages: "files", // `single`, `items` or `files`
     exclude: ["./test"],
   },
+  etherscan: {
+    // Your API key for Etherscan
+    // Obtain one at https://etherscan.io/
+    apiKey: process.env.ETHERSCAN_API_KEY || "",
+  },
 }
 
 export default config

package.json

@@ -58,6 +58,7 @@
     "typescript": "^4.4.4"
   },
   "dependencies": {
+    "@nomicfoundation/hardhat-verify": "^2.1.0",
     "@openzeppelin/contracts": "~4.5.0",
     "@openzeppelin/contracts-upgradeable": "~4.5.2",
     "@thesis/solidity-contracts": "github:thesis/solidity-contracts#4985bcf"