Support custom etherscan network

[drortirosh]

Ethers Version

5.6.6

Describe the Problem

Currently, EtherscanProvider requires exact network name (mainnet/goerli/ropsten/rinkeby/kovan and lately added optimism)

However, many more networks support the etherscan API, and it is a shame that we need an explicit modification to to the stack to support them.

Suggestion

The provider should accept a URL, much like a normal provider supports either network name or URL.
It is up to the developer to make sure the URL is a valid etherscan API , and that the API key matches this etherscan service.

Code Snippet

No response

Contract ABI

No response

Errors

No response

Environment

No response

Environment (Other)

No response

[ricmoo]

This is already supported through the use of sub-classing in v5.

For an example see: https://github.com/ethers-io/ancillary-bsc/blob/main/src.ts/bscscan-provider.ts

In v6, this is specified by the network, by attaching an EtherscanPlugin (see this example: https://github.com/ethers-io/ethers.js/blob/v6-beta/packages/providers/src.ts/common-networks.ts#L85)