use hardhat config from hardhat runtime environment

[xiaosongfu]

Why not read hardhat config from hardhat-runtime-environment directly? I can't understand😭, so i create this PR

with the changes, we just need:

let client = new MetamaskClient();

[xiaosongfu]

And then we can do more changes for more convenient use：

In our plugin:

declare module "hardhat/types/runtime" {
  export interface HardhatRuntimeEnvironment {
    metamask: MetamaskClient;
  }
}

extendEnvironment((hre) => {
  hre.metamask = new MetamaskClient();
});

In user's deploy scripts:

const mockPoints = await ethers.deployContract("MockPoints", {
 signer: await hre.metamask.getSigner(),
});
await mockPoints.waitForDeployment();
hre.metamask.close();