feat(cli): Add web3signer KeySource

[tsnewnami]

Addresses: #365 towards #502

Overview

This PR adds support for consensys' Web3Signer as remote signer for generating BLS key delegations.
This will allow for the listing and signing of delegate messages using Web3Signer.

Tests have been added which follow a similar pattern to Dirk.
E.g. cargo test --package bolt --bin bolt -- common::web3signer::tests --exact --show-output --ignored

The readme has been updated to capture these changes README here.

Note: that web3signer must be built from source as the commitboost API has not been released

[tsnewnami]

Hey team, I think this is a good stage for milestone check-in to receive some early feedback. There are still some small changes I need to make such as figuring out the TLS on reqwest and merge conflicts. Though the main meat of functionality should be there.

Thank you 🙏

[merklefruit]

Hey @Edwardjes thanks a lot for this draft. Will take a look shortly and will get back as soon as I have a review ready

[tsnewnami]

Merge conflicts and TLS fixed. Have taken this out of draft now 🙏

[merklefruit]

This looks great! I've tested it locally with web3signer built from source and the tests worked and I was able to generate a delegation from this.

Amazing work @Edwardjes!

[thedevbirb]

Looks great! Thanks a lot for the contribution. I have just two nits.
I defer to @merklefruit for merging

[merklefruit]

Thanks a lot @Edwardjes 🚀
CI is red due to some secrets configuration stuff but this is gtg.