JS library support to Ethers.js v6

[AndreMiras]

The JavaScript library seems to only support Ethers.js v5 at the moment.
It would be nice to have support for Ethers v6.
This is related to #427, but not a dup, as #427 suggest to document the fact that v5 only is currently supported, while I'd like to have support for v6

[AndreMiras]

I guess I should be using zksync-ethers@6 instead.
https://docs.zksync.io/build/sdks/js/zksync-ethers/migration.html
Maybe we can add a note on the README suggesting the zksync JS library is deprecated.