getNetwork allow optional chainId and network name

[The function already exists](https://github.com/Earnifi/essential-eth/blob/13ff58c68f3602c2f172e47f3ce118bd298872f5/src/providers/BaseProvider.ts#L41) in `essential-eth`, but it does not accept any params. The params should be optional and introduce a new type [`Networkish`](https://docs.ethers.io/v5/api/providers/types/#providers-Networkish)

https://docs.ethers.io/v5/api/providers/#providers--networks

```js
// By Chain Name
getNetwork("homestead");
// {
// chainId: 1,
// ensAddress: '0x00000000000C2E074eC69A0dFb2997BA6C7d2e1e',
// name: 'homestead'
// }

// By Chain ID
getNetwork(1);
// {
// chainId: 1,
// ensAddress: '0x00000000000C2E074eC69A0dFb2997BA6C7d2e1e',
// name: 'homestead'
// }
```