hardhat keystore rename

### Describe the feature

```
hardhat keystore rename KEY_1 KEY_2
```

equivalent of doing
```
hardhat keystore get KEY_1
// copy the value of KEY_1
hardhat keystore set KEY_2
// paste the copied value
```

why: i've been renaming config variables recently and i think this might come in handy for other people too

### Search terms

_No response_