Support cb-signer

[yorickdowne]

What I did

Add support for cb-signer. For better UX, a Python init script does some sanity checking of the config and sets the variables correctly for different clients.

(not mandatory) A picture of a cute animal, if possible in relation to what you did

[yorickdowne]

On hold for now. It isn't clear what part of the ecosystem would be enabled by using cb-signer, and cb-signer itself isn't baked yet.

[yorickdowne]

This would be for eth-gas. Have to confirm that eth-gas uses standard commit-boost signer now, and how to configure https://github.com/ethgas-developer/ethgas-preconf-commit-boost-module

They use a relay now. Rather than do this twice, look at this idea post-Glamsterdam

It might be best to require web3signer when using eth-gas, ignore cb-signer entirely. And then ethgas would need to have a way to work with web3signer

From the CB docs, the cb_signer doesn't run when using web3signer :
"Web3Signer implements the same API as Commit-Boost, so there's no need to set up a Signer module. The parameters needed for the remote signer are:

[signer.remote]
url = "https://remote.signer.url

"